avformat/avio: fix memory leak in url_find_protocol

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/avio.c

@@ -282,6 +282,7 @@ static const struct URLProtocol *url_find_protocol(const char *filename)
             return up;
         }
     }
+    av_freep(&protocols);
 
     return NULL;
 }