SDL_test_common.c: minor warning fix (SDL_AudioDeviceID is unsigned)

src/test/SDL_test_common.c

@@ -1343,7 +1343,7 @@ SDLTest_CommonInit(SDLTest_CommonState *state)
         }
 
         state->audio_id = SDL_OpenAudioDevice(NULL, 0, &state->audiospec, NULL, 0);
-        if (state->audio_id <= 0) {
+        if (!state->audio_id) {
             SDL_Log("Couldn't open audio: %s\n", SDL_GetError());
             return SDL_FALSE;
         }