gfx/sixel,network: reuse menu frame buffer across set_texture_frame calls

Both drivers unconditionally free'd menu_frame and set it to NULL
before a subsequent size-comparison check, making the "only reallocate
if size changed" branch dead. Every menu frame triggered a full
free+malloc+memcpy round-trip on a buffer that typically never changes
size after the first call.

Replace with a cached-capacity realloc pattern: allocate or grow only
when the required size exceeds the current capacity; otherwise reuse
the existing buffer. On realloc failure the previous frame is kept
intact (the original free+malloc sequence would have lost it).

These drivers store their menu state in file-scope static globals
rather than struct members (unlike e.g. fpga/caca which carry the
state on the driver handle). The globals survive across driver
teardown/re-init, so the new capacity variable is explicitly reset
to 0 in the *_free path alongside clearing the pointer to NULL;
without that, re-init after teardown could skip the realloc on a
same-or-smaller first frame and memcpy into the freed pointer.

Thread-safety: set_texture_frame and the frame read-site both run on
the video thread (threaded video) or main thread (non-threaded),
sequentially within the same loop iteration. No synchronization
required, none added. The realloc pattern additionally closes a
transient NULL window that existed between the free and malloc in
the original code.

Author: LibretroAdmin

gfx/drivers/network_gfx.c

@@ -62,6 +62,7 @@ typedef struct network
 } network_video_t;
 
 static unsigned char *network_menu_frame = NULL;
+static size_t network_menu_frame_cap     = 0;
 static unsigned network_menu_width       = 0;
 static unsigned network_menu_height      = 0;
 static unsigned network_menu_pitch       = 0;
@@ -371,6 +372,7 @@ static void network_gfx_free(void *data)
       free(network_video_temp_buf);
 
    network_menu_frame     = NULL;
+   network_menu_frame_cap = 0;
    network_video_temp_buf = NULL;
 
    font_driver_free_osd();
@@ -391,32 +393,29 @@ static void network_set_texture_frame(void *data,
       const void *frame, bool rgb32, unsigned width, unsigned height,
       float alpha)
 {
-   unsigned pitch = width * 2;
+   unsigned pitch = width * (rgb32 ? 4 : 2);
+   size_t   required;
 
-   if (rgb32)
-      pitch = width * 4;
-
-   if (network_menu_frame)
-   {
-      free(network_menu_frame);
-      network_menu_frame = NULL;
-   }
+   if (!frame || !width || !height || !pitch)
+      return;
 
-   if (     !network_menu_frame
-         || (network_menu_width  != width)
-         || (network_menu_height != height)
-         || (network_menu_pitch  != pitch))
-      if (pitch && height)
-         network_menu_frame = (unsigned char*)malloc(pitch * height);
+   required = (size_t)pitch * (size_t)height;
 
-   if (network_menu_frame && frame && pitch && height)
+   if (required > network_menu_frame_cap)
    {
-      memcpy(network_menu_frame, frame, pitch * height);
-      network_menu_width  = width;
-      network_menu_height = height;
-      network_menu_pitch  = pitch;
-      network_menu_bits   = rgb32 ? 32 : 16;
+      unsigned char *tmp = (unsigned char*)realloc(
+            network_menu_frame, required);
+      if (!tmp)
+         return;                        /* keep previous frame intact */
+      network_menu_frame     = tmp;
+      network_menu_frame_cap = required;
    }
+
+   memcpy(network_menu_frame, frame, required);
+   network_menu_width  = width;
+   network_menu_height = height;
+   network_menu_pitch  = pitch;
+   network_menu_bits   = rgb32 ? 32 : 16;
 }
 
 static void network_get_video_output_size(void *data,

gfx/drivers/sixel_gfx.c

@@ -137,6 +137,7 @@ font_renderer_t sixel_font = {
  */
 
 static unsigned char *sixel_menu_frame = NULL;
+static size_t sixel_menu_frame_cap     = 0;
 static unsigned sixel_menu_width       = 0;
 static unsigned sixel_menu_height      = 0;
 static unsigned sixel_menu_pitch       = 0;
@@ -532,6 +533,7 @@ static void sixel_gfx_free(void *data)
       free(sixel_menu_frame);
       sixel_menu_frame = NULL;
    }
+   sixel_menu_frame_cap = 0;
 
    if (sixel_temp_buf)
    {
@@ -566,29 +568,29 @@ static void sixel_set_texture_frame(void *data,
       const void *frame, bool rgb32, unsigned width, unsigned height,
       float alpha)
 {
-   unsigned pitch = width * 2;
+   unsigned pitch = width * (rgb32 ? 4 : 2);
+   size_t   required;
 
-   if (rgb32)
-      pitch = width * 4;
-
-   if (sixel_menu_frame)
-   {
-      free(sixel_menu_frame);
-      sixel_menu_frame = NULL;
-   }
+   if (!frame || !width || !height || !pitch)
+      return;
 
-   if (!sixel_menu_frame || sixel_menu_width != width || sixel_menu_height != height || sixel_menu_pitch != pitch)
-      if (pitch && height)
-         sixel_menu_frame = (unsigned char*)malloc(pitch * height);
+   required = (size_t)pitch * (size_t)height;
 
-   if (sixel_menu_frame && frame && pitch && height)
+   if (required > sixel_menu_frame_cap)
    {
-      memcpy(sixel_menu_frame, frame, pitch * height);
-      sixel_menu_width  = width;
-      sixel_menu_height = height;
-      sixel_menu_pitch  = pitch;
-      sixel_menu_bits   = rgb32 ? 32 : 16;
+      unsigned char *tmp = (unsigned char*)realloc(
+            sixel_menu_frame, required);
+      if (!tmp)
+         return;                        /* keep previous frame intact */
+      sixel_menu_frame     = tmp;
+      sixel_menu_frame_cap = required;
    }
+
+   memcpy(sixel_menu_frame, frame, required);
+   sixel_menu_width  = width;
+   sixel_menu_height = height;
+   sixel_menu_pitch  = pitch;
+   sixel_menu_bits   = rgb32 ? 32 : 16;
 }
 
 static void sixel_get_video_output_size(void *data,