h264: dont stop parsing NALs without cleanup on DPC.

Fixes a deadlock with frame threads

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -3975,7 +3975,7 @@ again:
                 hx->inter_gb_ptr = &hx->inter_gb;
 
                 av_log(h->s.avctx, AV_LOG_ERROR, "Partitioned H.264 support is incomplete\n");
-                return AVERROR_PATCHWELCOME;
+                break;
 
                 if (hx->redundant_pic_count == 0 &&
                     hx->intra_gb_ptr &&