SDL_GameControllerGetAppleSFSymbolsNameForAxis() returns NULL if the symbol isn't found

(cherry picked from commit 627e15871a1c48441e423fe1b6c3d8098ac9c3c8)

src/joystick/SDL_gamecontroller.c

@@ -3280,10 +3280,11 @@ const char *SDL_GameControllerGetAppleSFSymbolsNameForAxis(SDL_GameController *g
     }
     SDL_UnlockJoysticks();
 
-    return retval;
-#else
-    return NULL;
+    if (retval && *retval) {
+        return retval;
+    }
 #endif
+    return NULL;
 }
 
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