ffserver: dont leak pb_buffer

ffserver.c

@@ -2254,6 +2254,7 @@ static int http_prepare_data(HTTPContext *c)
                         c->state = HTTPSTATE_SEND_DATA_TRAILER;
                     }
 
+                    av_freep(&c->pb_buffer);
                     len = avio_close_dyn_buf(ctx->pb, &c->pb_buffer);
                     c->cur_frame_bytes = len;
                     c->buffer_ptr = c->pb_buffer;