avcodec/avcodec: Sanitize options before using them

This is how it is supposed to happen, yet when using frame threading,
the codec's init function has been called before preinit. This can lead
to crashes when e.g. using unsupported lowres values for decoders
together with frame threading.

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

libavcodec/avcodec.c

@@ -315,6 +315,13 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
         avctx->time_base.den = avctx->sample_rate;
     }
 
+    if (av_codec_is_encoder(avctx->codec))
+        ret = ff_encode_preinit(avctx);
+    else
+        ret = ff_decode_preinit(avctx);
+    if (ret < 0)
+        goto free_and_end;
+
     if (!HAVE_THREADS)
         av_log(avctx, AV_LOG_WARNING, "Warning: not compiled with thread support, using thread emulation\n");
 
@@ -336,13 +343,6 @@ int attribute_align_arg avcodec_open2(AVCodecContext *avctx, const AVCodec *code
     if (!HAVE_THREADS && !(codec->caps_internal & FF_CODEC_CAP_AUTO_THREADS))
         avctx->thread_count = 1;
 
-    if (av_codec_is_encoder(avctx->codec))
-        ret = ff_encode_preinit(avctx);
-    else
-        ret = ff_decode_preinit(avctx);
-    if (ret < 0)
-        goto free_and_end;
-
     if (   avctx->codec->init && (!(avctx->active_thread_type&FF_THREAD_FRAME)
         || avci->frame_thread_encoder)) {
         ret = avctx->codec->init(avctx);