avcodec/vvcdec: ensure every CTU belongs to a slice

According to section 6.3.3 "Spatial or component-wise partitionings,"
CTUs should fully cover slices with no overlaps, gaps, or additions.
No overlaps are ensured by task_init_parse.
No gaps and no additions are ensured by this patch.

Co-authored-by: Frank Plowman <post@frankplowman.com>
(cherry picked from commit 5c5a08ecb5)

libavcodec/vvc/thread.c

@@ -822,6 +822,13 @@ int ff_vvc_frame_submit(VVCContext *s, VVCFrameContext *fc)
             }
         }
     }
+    for (int rs = 0; rs < ft->ctu_count; rs++) {
+        const VVCTask *t = ft->tasks + rs;
+        if (!t->sc) {
+            av_log(s->avctx, AV_LOG_ERROR, "frame %5d, CTU(%d, %d) not belong to any slice\r\n", (int)fc->decode_order, t->rx, t->ry);
+            return AVERROR_INVALIDDATA;
+        }
+    }
     frame_thread_add_score(s, ft, 0, 0, VVC_TASK_STAGE_INIT);
 
     return 0;