Do not check for decoder error in the demux thread

That was only an optimization, and it fails thread-safety.
In any case, a failed decoder will still dequeue (and discard) blocks.

src/input/decoder.c

@@ -337,7 +337,7 @@ void input_DecoderDecode( decoder_t *p_dec, block_t *p_block )
     if( p_owner->p_input->p->b_out_pace_control )
     {
         /* FIXME !!!!! */
-        while( vlc_object_alive( p_dec ) && !p_dec->b_error &&
+        while( vlc_object_alive( p_dec ) &&
                block_FifoCount( p_owner->p_fifo ) > 10 )
         {
             msleep( 1000 );