twn_textures: lock cache when adding requests

src/twn_textures.c

@@ -509,13 +509,13 @@ static TextureKey textures_load(TextureCache *cache, const char *path) {
 
     /* place a dummy for future lookups to know it will be loaded */
     /* as well as a place for worker to fill in */
+    SDL_LockMutex(textures_load_mutex);
     shput(cache->hash, path, (Texture){0});
 
     /* append a new request, use stable indices */
     struct TextureLoadRequest const request = {
         .index = shlenu(cache->hash) - 1,
     };
-    SDL_LockMutex(textures_load_mutex);
     arrpush(texture_load_queue, request);
     SDL_UnlockMutex(textures_load_mutex);