use reversePathTo in place of addPathReverse

Path ops was using addPathReverse, instead of reversePathTo.
The former adds a moveTo always, and the latter requires
that the caller add the moveTo if needed.

Simplify the reversePathTo implementation.

R=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2481463002

Review-Url: https://codereview.chromium.org/2481463002
diff --git a/src/pathops/SkPathWriter.cpp b/src/pathops/SkPathWriter.cpp
index c94809e..9893a50 100644
--- a/src/pathops/SkPathWriter.cpp
+++ b/src/pathops/SkPathWriter.cpp
@@ -306,7 +306,7 @@
                         first ? SkPath::kAppend_AddPathMode : SkPath::kExtend_AddPathMode);
             } else {
                 SkASSERT(!first);
-                fPathPtr->reverseAddPath(contour);
+                fPathPtr->reversePathTo(contour);
             }
             if (first) {
                 first = false;