avcodec/avcodec: Make sanity check stricter

If an AVCodec has a private class, its priv_data_size must be > 0
and at the end of a successful call to avcodec_open2()
the AVCodecContext's priv_data must exist and its first element
must be a pointer to said AVClass. This should not be conditional
on priv_data_size being > 0 (which is tested by FATE) or
on the private context having been successfully allocated
(which has to have happened at that point). So remove these
preconditions to make the test stricter.

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

libavcodec/avcodec.c

@@ -364,9 +364,8 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
             avctx->time_base = av_inv_q(av_mul_q(avctx->framerate, (AVRational){avctx->ticks_per_frame, 1}));
 #endif
     }
-    if (codec->priv_data_size > 0 && avctx->priv_data && codec->priv_class) {
+    if (codec->priv_class)
         av_assert0(*(const AVClass **)avctx->priv_data == codec->priv_class);
-    }
 
 end:
     unlock_avcodec(codec);