avcodec/vc1: Don't check for AVCodecContext.codec

This check has been added in c617bed34f,
merging ee769c6a7c to fix
a possible segfault if AVCodecContext.codec is not set
as it may be during parsing. While this fixes the segfault,
it has the unfortunate side effect that it makes the output
of the parser dependent on whether a decoder is set (and
ultimately available). The fix later applied in
5d2be71b9e does not have this
downside and makes checking AVCodecContext.codec superfluous.
So remove this check.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/vc1.c

@@ -632,8 +632,6 @@ int ff_vc1_parse_frame_header(VC1Context *v, GetBitContext* gb)
     v->fcm = PROGRESSIVE;
     if (v->finterpflag)
         v->interpfrm = get_bits1(gb);
-    if (!v->s.avctx->codec)
-        return -1;
     if (v->s.avctx->codec_id == AV_CODEC_ID_MSS2)
         v->respic   =
         v->rangered =