[skottie] Fix analytical mask fill type

Sksg::Merge needs to preserve the fill type of the first path appended
in the stack.

Theoretically, one could append multiple paths with different fill types
using sksg::Merge, but in practice Skottie should never do that (append
mode with invertible shape only used for the very first mask in a stack).

TBR=
Change-Id: Ie9ac9187cc1c8baaae2bef439313a7700407f04a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/303582
Reviewed-by: Florin Malita <[email protected]>
Commit-Queue: Florin Malita <[email protected]>

Author: fmalita

modules/sksg/src/SkSGMerge.cpp

@@ -68,17 +68,26 @@ SkRect Merge::onRevalidate(InvalidationController* ic, const SkMatrix& ctm) {
     fMerged.reset();
     bool in_builder = false;
 
+    auto append = [&](const SkPath& path) {
+        if (in_builder) {
+            builder.resolve(&fMerged);
+            in_builder = false;
+        }
+
+        if (fMerged.isEmpty()) {
+            // First merge path determines the fill type.
+            fMerged = path;
+        } else {
+            fMerged.addPath(path);
+        }
+    };
+
     for (const auto& rec : fRecs) {
         rec.fGeo->revalidate(ic, ctm);
 
-        // Merge is not currently supported by SkOpBuidler.
         if (rec.fMode == Mode::kMerge) {
-            if (in_builder) {
-                builder.resolve(&fMerged);
-                in_builder = false;
-            }
-
-            fMerged.addPath(rec.fGeo->asPath());
+            // Merge (append) is not supported by SkOpBuidler.
+            append(rec.fGeo->asPath());
             continue;
         }