fix bugs found by computing flat clips in 800K skps

src/pathops/SkPathOpsTriangle.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPathOpsTriangle.h"
 
 // http://www.blackpawn.com/texts/pointinpoly/default.html
 // return true if pt is inside triangle; false if outside or on the line
 bool SkDTriangle::contains(const SkDPoint& pt) const {
 // Compute vectors
     SkDVector v0 = fPts[2] - fPts[0];
     SkDVector v1 = fPts[1] - fPts[0];
     SkDVector v2 = pt - fPts[0];
 
 // Compute dot products
     double dot00 = v0.dot(v0);
     double dot01 = v0.dot(v1);
     double dot02 = v0.dot(v2);
     double dot11 = v1.dot(v1);
     double dot12 = v1.dot(v2);
 
 // original code doesn't handle degenerate input; isn't symmetric with inclusion of corner pts;
-// introduces necessary error with divide; doesn't short circuit on early answer
+// introduces error with divide; doesn't short circuit on early answer
 #if 0
 // Compute barycentric coordinates
     double invDenom = 1 / (dot00 * dot11 - dot01 * dot01);
     double u = (dot11 * dot02 - dot01 * dot12) * invDenom;
     double v = (dot00 * dot12 - dot01 * dot02) * invDenom;
 
 // Check if point is in triangle
     return (u >= 0) && (v >= 0) && (u + v <= 1);
 #else
     double w = dot00 * dot11 - dot01 * dot01;
     if (w == 0) {
         return false;
     }
     double wSign = w < 0 ? -1 : 1;
     double u = (dot11 * dot02 - dot01 * dot12) * wSign;
     if (u <= 0) {
         return false;
     }
     double v = (dot00 * dot12 - dot01 * dot02) * wSign;
     if (v <= 0) {
         return false;
     }
     return u + v < w * wSign;
 #endif
 }