avcodec: force thread count to 1 when disabling due to ffmpeg-hw use.

modules/codec/avcodec/video.c

@@ -382,12 +382,14 @@ int InitVideoDec( decoder_t *p_dec, AVCodecContext *p_context,
         {
             msg_Warn( p_dec, "threaded frame decoding is not compatible with ffmpeg-hw, disabled" );
             p_sys->p_context->thread_type &= ~FF_THREAD_FRAME;
+            p_sys->p_context->thread_count = 1;
         }
         if( ( p_sys->p_context->thread_type & FF_THREAD_SLICE ) &&
             ( i_codec_id == CODEC_ID_MPEG1VIDEO || i_codec_id == CODEC_ID_MPEG2VIDEO ) )
         {
             msg_Warn( p_dec, "threaded slice decoding is not compatible with ffmpeg-hw, disabled" );
             p_sys->p_context->thread_type &= ~FF_THREAD_SLICE;
+            p_sys->p_context->thread_count = 1;
         }
 #endif
         p_sys->p_context->get_format = ffmpeg_GetFormat;