metadata: SDL_GetAppMetadataProperty() now uses SDL_GetExeName().

(for SDL_PROP_APP_METADATA_NAME_STRING if unset. If SDL_GetExeName() returns
NULL, it'll fallback to good ol' "SDL Application", as usual.)

Fixes #15692.

src/SDL.c

@@ -169,7 +169,10 @@ const char *SDL_GetAppMetadataProperty(const char *name)
     }
     if (!value || !*value) {
         if (SDL_strcmp(name, SDL_PROP_APP_METADATA_NAME_STRING) == 0) {
-            value = "SDL Application";
+            value = SDL_GetExeName();
+            if (!value) {
+                value = "SDL Application";
+            }
         } else if (SDL_strcmp(name, SDL_PROP_APP_METADATA_TYPE_STRING) == 0) {
             value = "application";
         }