buffersrc: Fix resource leak on error

Bug-Id: CID 1267902
CC: libav-stable@libav.org
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>

libavfilter/buffersrc.c

@@ -195,6 +195,7 @@ do {                                                                    \
     ref_out = av_buffer_create(data, data_size, compat_unref_buffer,    \
                                dummy_ref, 0);                           \
     if (!ref_out) {                                                     \
+        av_freep(&dummy_ref);                                           \
         av_frame_unref(frame);                                          \
         ret = AVERROR(ENOMEM);                                          \
         goto fail;                                                      \