Destroy condition variable on frames destruction

A condition variable was init for the "struct frames", but was never destroyed.

app/src/frames.c

@@ -37,6 +37,7 @@ error_0:
 
 void frames_destroy(struct frames *frames) {
     SDL_DestroyMutex(frames->mutex);
+    SDL_DestroyCond(frames->rendering_frame_consumed_cond);
     av_frame_free(&frames->rendering_frame);
     av_frame_free(&frames->decoding_frame);
 }