don't create zero length intervals

gm/bug530095.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 #include "SkPath.h"
 #include "SkDashPathEffect.h"
@@ skipping 28 matching lines @@
     canvas->translate(0, 400);
     canvas->drawPath(path1, paint);
     canvas->restore();
 
     paint.setStrokeWidth(0.26f);
     paint.setPathEffect(SkDashPathEffect::Create(smIntervals, smIntervalCount, 0))->unref();
     canvas->scale(100, 100);
     canvas->translate(4, 4);
     canvas->drawPath(path2, paint);
 }
+
+DEF_SIMPLE_GM(bug591993, canvas, 40, 140) {
+    SkPaint p;
+    p.setColor(SK_ColorRED);
+    p.setAntiAlias(true);
+    p.setStyle(SkPaint::kStroke_Style);
+    p.setStrokeCap(SkPaint::kRound_Cap);
+    p.setStrokeWidth(10);
+    SkScalar intervals[] = { 100, 100 };
+    SkPathEffect* dash = SkDashPathEffect::Create(intervals, SK_ARRAY_COUNT(intervals), 100);
+    p.setPathEffect(dash)->unref();
+    canvas->drawLine(20, 20, 120, 20, p);
+}