lavc/avcodec: simplify codec id/type validity checking

On entry to avcodec_open2(), the AVCodecContext type and id either have
to be UNKNOWN/NONE or have to match the codec to be used.

libavcodec/avcodec.c

@@ -158,17 +158,15 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
         codec = avctx->codec;
     codec2 = ffcodec(codec);
 
-    if ((avctx->codec_type == AVMEDIA_TYPE_UNKNOWN || avctx->codec_type == codec->type) &&
+    if ((avctx->codec_type != AVMEDIA_TYPE_UNKNOWN && avctx->codec_type != codec->type) ||
-        avctx->codec_id == AV_CODEC_ID_NONE) {
+        (avctx->codec_id   != AV_CODEC_ID_NONE     && avctx->codec_id   != codec->id)) {
-        avctx->codec_type = codec->type;
-        avctx->codec_id   = codec->id;
-    }
-    if (avctx->codec_id != codec->id || (avctx->codec_type != codec->type &&
-                                         avctx->codec_type != AVMEDIA_TYPE_ATTACHMENT)) {
         av_log(avctx, AV_LOG_ERROR, "Codec type or id mismatches\n");
         return AVERROR(EINVAL);
     }
-    avctx->codec = codec;
+
+    avctx->codec_type = codec->type;
+    avctx->codec_id   = codec->id;
+    avctx->codec      = codec;
 
     if (avctx->extradata_size < 0 || avctx->extradata_size >= FF_MAX_EXTRADATA_SIZE)
         return AVERROR(EINVAL);