disallow -4 pointer

src/core/SkPath.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include <cmath>
 #include "SkBuffer.h"
 #include "SkCubicClipper.h"
@@ skipping 1765 matching lines @@
 }
 
 SkPath::Iter::Iter(const SkPath& path, bool forceClose) {
     this->setPath(path, forceClose);
 }
 
 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);
     fNeedClose = false;
     fSegmentState = kEmptyContour_SegmentState;
 }
 
 bool SkPath::Iter::isClosedContour() const {
     if (fVerbs == nullptr || fVerbs == fVerbStop) {
         return false;
@@ skipping 1566 matching lines @@
         *direction = SkPath::kCW_Direction;
         *start = firstDir;
     } else {
         SkASSERT(((secondDir + 1) & 0b11) == firstDir);
         *direction = SkPath::kCCW_Direction;
         *start = secondDir;
     }
     *rect = tempRect;
     return true;
 }