platform_darwin: fix URLForResource filter dir extraction

GCC on 10.5 SDK emitted:

  platform_darwin.m:465: warning: passing argument 2 of strlcpy
  from incompatible pointer type

ROOT CAUSE: the expression [[url baseURL] fileSystemRepresentation]
had two separate problems.

1. LOGIC BUG (preexisting, silent): -[NSURL baseURL] returns the URL
   that the receiver was constructed relative to.  For URLs made
   absolutely - which is what -[NSBundle URLForResource:withExtension:
   subdirectory:] returns - baseURL is nil.  Messaging
   -fileSystemRepresentation on nil returns (const char *)0, and
   strlcpy then reads from a NULL source pointer.  This was a latent
   bug that predates this audit.

2. COMPILE WARNING (the reported symptom): on the 10.5 SDK, NSURL
   doesn't declare -fileSystemRepresentation (that selector was only
   added to NSURL in 10.9).  GCC 4.0 resolves the selector against
   NSString's declaration - which returns const char * and would
   match strlcpy - but warns about incompatible pointer type because
   the receiver [url baseURL] is typed NSURL*, not NSString*.

FIX: replace both sites with

  [[[url path] stringByDeletingLastPathComponent] UTF8String]

All three selectors are 10.0-era NSString methods, unambiguous, and
warning-clean.  Also semantically correct: URLForResource:nil with
a subdirectory returns the URL of the *first matching file* in that
subdirectory; what we want is its containing directory, which is
exactly what stringByDeletingLastPathComponent gives us.

The pattern matches ui/drivers/ui_cocoa.m:193 which already does
[url.path UTF8String] for the same NSURL-to-C-string conversion.

No behavioral change on bundles that don't ship inline filter files
(the URLForResource: call returns nil and the fill_pathname_join
fallback runs as before).  On bundles that do, the audio/video
filter dirs will now resolve to the correct directory instead of
dereferencing NULL.

Author: LibretroAdmin

frontend/drivers/platform_darwin.m

@@ -455,14 +455,25 @@ static void frontend_darwin_get_env(int *argc, char *argv[],
    if ([[NSBundle mainBundle] respondsToSelector:url_for_resource_sel])
       url = [[NSBundle mainBundle] URLForResource:nil withExtension:@"dsp" subdirectory:@"filters/audio"];
    if (url)
-       strlcpy(g_defaults.dirs[DEFAULT_DIR_AUDIO_FILTER], [[url baseURL] fileSystemRepresentation],  sizeof(g_defaults.dirs[DEFAULT_DIR_AUDIO_FILTER]));
+       /* URLForResource: with a nil name returns a URL pointing at
+        * the first matching .dsp file.  What we want is the directory
+        * it lives in, so strip the last path component.
+        *
+        * The previous code used [[url baseURL] fileSystemRepresentation],
+        * which was wrong on two counts: -baseURL returns nil for URLs
+        * constructed absolutely (which is what URLForResource: returns),
+        * so the result was a NULL source pointer into strlcpy; and on
+        * pre-10.9 SDKs NSURL doesn't declare -fileSystemRepresentation,
+        * so GCC resolved the selector against NSString's version with
+        * an incompatible-receiver warning. */
+       strlcpy(g_defaults.dirs[DEFAULT_DIR_AUDIO_FILTER], [[[url path] stringByDeletingLastPathComponent] UTF8String], sizeof(g_defaults.dirs[DEFAULT_DIR_AUDIO_FILTER]));
    else
        fill_pathname_join(g_defaults.dirs[DEFAULT_DIR_AUDIO_FILTER], application_data, "filters/audio", sizeof(g_defaults.dirs[DEFAULT_DIR_AUDIO_FILTER]));
    url = nil;
    if ([[NSBundle mainBundle] respondsToSelector:url_for_resource_sel])
       url = [[NSBundle mainBundle] URLForResource:nil withExtension:@"filt" subdirectory:@"filters/video"];
    if (url)
-       strlcpy(g_defaults.dirs[DEFAULT_DIR_VIDEO_FILTER], [[url baseURL] fileSystemRepresentation],  sizeof(g_defaults.dirs[DEFAULT_DIR_VIDEO_FILTER]));
+       strlcpy(g_defaults.dirs[DEFAULT_DIR_VIDEO_FILTER], [[[url path] stringByDeletingLastPathComponent] UTF8String], sizeof(g_defaults.dirs[DEFAULT_DIR_VIDEO_FILTER]));
    else
        fill_pathname_join(g_defaults.dirs[DEFAULT_DIR_VIDEO_FILTER], application_data, "filters/video", sizeof(g_defaults.dirs[DEFAULT_DIR_VIDEO_FILTER]));
    fill_pathname_join(g_defaults.dirs[DEFAULT_DIR_CORE_INFO], application_data, "info", sizeof(g_defaults.dirs[DEFAULT_DIR_CORE_INFO]));