gfx/vulkan: NULL-check instance_extensions / instance_layers malloc in create_instance_wrapper

vulkan_context_create_instance_wrapper malloc()s two pointer arrays -
instance_extensions and instance_layers - then immediately memcpy's
into both and assigns them into the VkInstanceCreateInfo that gets
passed to vkCreateInstance:

    const char **instance_extensions = (const char**)malloc(...);
    const char **instance_layers     = (const char**)malloc(...);
    ...
    memcpy((void*)instance_extensions, ...);
    memcpy((void*)instance_layers,     ...);
    info.ppEnabledExtensionNames     = instance_extensions;
    info.ppEnabledLayerNames         = instance_layers;

Neither malloc is NULL-checked before those memcpys, so an OOM on
either one segfaults on the memcpy.  An OOM on only one would be
caught by the 'end' label free (both frees are there, and free(NULL)
is defined as a no-op), but only if we actually reach 'end' rather
than crashing on the memcpy.

Fix: after both mallocs, NULL-check both and 'goto end' on failure.
'instance' was pre-initialised to VK_NULL_HANDLE at the top of the
function, which is the correct error-return value for this API, so
the 'end' label cleanup already handles the rest of the function's
contract correctly.

These allocations are small (pointer arrays sized by the core's
extension / layer counts, typically a handful to a few dozen
entries), so OOM here is unlikely in practice.  Still worth
guarding - the payoff for a NULL check against a real crash is
asymmetric.

Thread-safety: unchanged.  Called from the Vulkan context init
path which runs on the video thread.

Author: LibretroAdmin

gfx/common/vulkan_common.c

@@ -902,6 +902,18 @@ static VkInstance vulkan_context_create_instance_wrapper(void *opaque, const VkI
    const char *required_extensions[3];
    uint32_t required_extension_count = 0;
 
+   /* Both mallocs must have succeeded before the memcpy / field
+    * assignments below dereference the buffers.  The 'end' label
+    * free()s both pointers; free(NULL) is a no-op, so if only one
+    * of the two succeeded it still gets reclaimed.  'instance' was
+    * pre-initialised to VK_NULL_HANDLE at the top of the function,
+    * which is the correct error-return value for this API. */
+   if (!instance_extensions || !instance_layers)
+   {
+      RARCH_ERR("[Vulkan] Out of memory allocating instance extension / layer arrays.\n");
+      goto end;
+   }
+
    memcpy((void*)instance_extensions, info.ppEnabledExtensionNames, info.enabledExtensionCount * sizeof(const char *));
    memcpy((void*)instance_layers,     info.ppEnabledLayerNames,     info.enabledLayerCount     * sizeof(const char *));
    info.ppEnabledExtensionNames     = instance_extensions;