avformat/oggparsevorbis: Use AV_DICT_DONT_STRDUP_VAL to avoid av_strdup

This will likely also fix CID 1452427, a false positive resulting from
Coverity thinking that av_dict_set() automatically frees its key and
value parameters (even without the AV_DICT_DONT_STRDUP_* flags).

(AV_DICT_APPEND and AV_DICT_DONT_STRDUP_VAL are compatible with each
other since a8c5b455, so we can reset this flag here. It has originally
been removed in 0dc66553 when appending was added.)
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/oggparsevorbis.c

@@ -177,9 +177,8 @@ int ff_vorbis_comment(AVFormatContext *as, AVDictionary **m,
                     av_dict_set(m, tt, ";", AV_DICT_APPEND);
                 }
                 av_dict_set(m, tt, ct,
-                            AV_DICT_DONT_STRDUP_KEY |
+                            AV_DICT_DONT_STRDUP_KEY | AV_DICT_DONT_STRDUP_VAL |
                             AV_DICT_APPEND);
-                av_freep(&ct);
             }
         }
     }