Do not set record to empty if it's already computed

Otherwise, the following test will fail:

./out/Debug/dm --config t8888 -m strokes_round

Bug: skia:
Change-Id: Ifc618fc42c6f387eae7b6aadd8424001c3e1464e
Reviewed-on: https://skia-review.googlesource.com/113440
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

src/core/SkCoverageDelta.h

@@ -203,7 +203,9 @@ struct SkDAARecord {
     void setEmpty() { fType = Type::kEmpty; }
     static inline void SetEmpty(SkDAARecord* record) { // record may be nullptr
 #ifdef SK_DEBUG
-        if (record) {
+        // If type != kToBeComputed, then we're in the draw phase and we shouldn't set it to empty
+        // because being empty in one tile does not imply emptiness in other tiles.
+        if (record && record->fType == Type::kToBeComputed) {
             record->setEmpty();
         }
 #endif