disallow -4 pointer

src/core/SkPath.cpp

Index: src/core/SkPath.cpp
diff --git a/src/core/SkPath.cpp b/src/core/SkPath.cpp
index f5b53fcc00e085785be61a23a0e9c601f891e6fb..508d1e4125678eb0bdf109d5b62822054c3e58cc 100644
--- a/src/core/SkPath.cpp
+++ b/src/core/SkPath.cpp
@@ -1783,7 +1783,10 @@ void SkPath::Iter::setPath(const SkPath& path, bool forceClose) {
     fPts = path.fPathRef->points();
     fVerbs = path.fPathRef->verbs();
     fVerbStop = path.fPathRef->verbsMemBegin();
-    fConicWeights = path.fPathRef->conicWeights() - 1; // begin one behind
+    fConicWeights = path.fPathRef->conicWeights();
+    if (fConicWeights) {
+      fConicWeights -= 1;  // begin one behind
+    }
     fLastPt.fX = fLastPt.fY = 0;
     fMoveTo.fX = fMoveTo.fY = 0;
     fForceClose = SkToU8(forceClose);