allow one zero length dash

src/effects/SkDashPathEffect.cpp

Index: src/effects/SkDashPathEffect.cpp
diff --git a/src/effects/SkDashPathEffect.cpp b/src/effects/SkDashPathEffect.cpp
index ced0aab69a9930efbbd216127f776dd5d8c2770d..7e7e48c7b3b54f15dd6141c611443488d29fe6f2 100644
--- a/src/effects/SkDashPathEffect.cpp
+++ b/src/effects/SkDashPathEffect.cpp
@@ -14,7 +14,7 @@
 
 SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, SkScalar phase)
         : fPhase(0)
-        , fInitialDashLength(0)
+        , fInitialDashLength(-1)
         , fInitialDashIndex(0)
         , fIntervalLength(0) {
     SkASSERT(intervals);
@@ -28,7 +28,7 @@ SkDashPathEffect::SkDashPathEffect(const SkScalar intervals[], int count, SkScal
     }
 
     // set the internal data members
-    SkDashPath::CalcDashParameters(phase, fIntervals, fCount,
+    fValidParameters = SkDashPath::CalcDashParameters(phase, fIntervals, fCount,
             &fInitialDashLength, &fInitialDashIndex, &fIntervalLength, &fPhase);
 }
 
@@ -38,6 +38,9 @@ SkDashPathEffect::~SkDashPathEffect() {
 
 bool SkDashPathEffect::filterPath(SkPath* dst, const SkPath& src,
                               SkStrokeRec* rec, const SkRect* cullRect) const {
+    if (!fValidParameters) {
+        return false;
+    }
     return SkDashPath::FilterDashPath(dst, src, rec, cullRect, fIntervals, fCount,
                                       fInitialDashLength, fInitialDashIndex, fIntervalLength);
 }
@@ -162,7 +165,7 @@ bool SkDashPathEffect::asPoints(PointData* results,
                                 const SkMatrix& matrix,
                                 const SkRect* cullRect) const {
     // width < 0 -> fill && width == 0 -> hairline so requiring width > 0 rules both out
-    if (fInitialDashLength < 0 || 0 >= rec.getWidth()) {
+    if (!fValidParameters || 0 >= rec.getWidth()) {
         return false;
     }