don't create zero length intervals

src/utils/SkDashPath.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDashPathPriv.h"
 #include "SkPathMeasure.h"
 #include "SkStrokeRec.h"
 
 static inline int is_even(int x) {
     return !(x & 1);
 }
 
 static SkScalar find_first_interval(const SkScalar intervals[], SkScalar phase,
                                     int32_t* index, int count) {
     for (int i = 0; i < count; ++i) {
-        if (phase > intervals[i]) {
-            phase -= intervals[i];
+        SkScalar gap = intervals[i];
+        if (phase > gap || (phase == gap && gap)) {
+            phase -= gap;
         } else {
             *index = i;
-            return intervals[i] - phase;
+            return gap - phase;
         }
     }
     // If we get here, phase "appears" to be larger than our length. This
     // shouldn't happen with perfect precision, but we can accumulate errors
     // during the initial length computation (rounding can make our sum be too
     // big or too small. In that event, we just have to eat the error here.
     *index = 0;
     return intervals[0];
 }
 
@@ skipping 287 matching lines @@
 bool SkDashPath::FilterDashPath(SkPath* dst, const SkPath& src, SkStrokeRec* rec,
                                 const SkRect* cullRect, const SkPathEffect::DashInfo& info) {
     SkScalar initialDashLength = 0;
     int32_t initialDashIndex = 0;
     SkScalar intervalLength = 0;
     CalcDashParameters(info.fPhase, info.fIntervals, info.fCount,
                        &initialDashLength, &initialDashIndex, &intervalLength);
     return FilterDashPath(dst, src, rec, cullRect, info.fIntervals, info.fCount, initialDashLength,
                           initialDashIndex, intervalLength);
 }