avformat/mov: don't read key_size bytes twice in the keys atom

We only support mdta as type, yet we were not skipping other types,
but rather reading key_size worth of bytes twice per entry.

Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit 5a06d3810e41134ee9c2941cc0b371da62b539db)

libavformat/mov.c

@@ -5048,6 +5048,7 @@ static int mov_read_keys(MOVContext *c, AVIOContext *pb, MOVAtom atom)
         key_size -= 8;
         if (type != MKTAG('m','d','t','a')) {
             avio_skip(pb, key_size);
+            continue;
         }
         c->meta_keys[i] = av_mallocz(key_size + 1);
         if (!c->meta_keys[i])