Fix Path#strokeBounds for open paths

Closes #1817

Author: lehni

src/path/Curve.js

@@ -867,8 +867,11 @@ statics: /** @lends Curve */{
             if (v1 < v0 != v1 < v3 && v2 < v0 != v2 < v3) {
                 // If the values of a curve are sorted, the extrema are simply
                 // the start and end point.
-                add(v0, padding);
-                add(v3, padding);
+                // Only add strokeWidth to bounds for points which lie within 0
+                // < t < 1. The corner cases for cap and join are handled in
+                // getStrokeBounds()
+                add(v0, 0);
+                add(v3, 0);
             } else {
                 // Calculate derivative of our bezier polynomial, divided by 3.
                 // Doing so allows for simpler calculations of a, b, c and leads
@@ -882,9 +885,7 @@ statics: /** @lends Curve */{
                     // with radii in getStrokeBounds()
                     tMin = /*#=*/Numerical.CURVETIME_EPSILON,
                     tMax = 1 - tMin;
-                // Only add strokeWidth to bounds for points which lie within 0
-                // < t < 1 The corner cases for cap and join are handled in
-                // getStrokeBounds()
+                // See above for an explanation of padding = 0 here:
                 add(v3, 0);
                 for (var i = 0; i < count; i++) {
                     var t = roots[i],

test/tests/Item_Bounds.js

@@ -790,11 +790,21 @@ test('group.internalBounds with child and child.applyMatrix = false (#1250)', fu
             'group.internalBounds after scaling item1');
 });
 
-test('#1561 item._globalMatrix on item after empty symbol', function(){
+test('item._globalMatrix on item after empty symbol (#1561)', function() {
     var symbol = new SymbolItem(new Path());
     symbol.opacity = 0.5;
     symbol.skew(10);
     var item = new Path.Circle(new Point(0,0), 10);
     view.update();
     equals(item._globalMatrix, new Matrix());
 });
+
+test('path.strokeBounds of open, circular arc (#1817)', function() {
+    var circle = new Path({
+        pathData: 'M8,16c0,-4.4 3.6,-8 8,-8c4.4,0 8,3.6 8,8',
+        strokeWidth: 8,
+        strokeColor: 'red'
+    });
+    equals(circle.strokeBounds, new Rectangle(4, 4, 24, 12),
+            'circle.strokeBounds');
+});