avcodec/ffv1enc: Fix memleaks on init failure

The FFV1 encoder has so far not cleaned up after itself in this case;
but it can be done easily by setting the FF_CODEC_CAP_INIT_CLEANUP flag.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/ffv1enc.c

@@ -1354,4 +1354,5 @@ AVCodec ff_ffv1_encoder = {
     .defaults       = ffv1_defaults,
 #endif
     .priv_class     = &ffv1_class,
+    .caps_internal  = FF_CODEC_CAP_INIT_CLEANUP,
 };