coerce arrowhead, arrowsize and startarrowsize only when it is needed

Author: apalchys

src/components/annotations/common_defaults.js

@@ -36,13 +36,18 @@ module.exports = function handleAnnotationCommonDefaults(annIn, annOut, fullLayo
 
     if(showArrow) {
         var arrowside = coerce('arrowside');
-        var arrowhead = coerce('arrowhead');
-        var arrowsize = coerce('arrowsize');
+        var arrowhead;
+        var arrowsize;
+
+        if(arrowside.indexOf('end') !== -1) {
+            arrowhead = coerce('arrowhead');
+            arrowsize = coerce('arrowsize');
+        }
 
         if(arrowside.indexOf('start') !== -1) {
             coerce('startarrowhead', arrowhead);
+            coerce('startarrowsize', arrowsize);
         }
-        coerce('startarrowsize', arrowsize);
         coerce('arrowcolor', borderOpacity ? annOut.bordercolor : Color.defaultLine);
         coerce('arrowwidth', ((borderOpacity && borderWidth) || 1) * 2);
         coerce('standoff');

src/components/annotations/draw_arrow_head.js

@@ -39,8 +39,8 @@ module.exports = function drawArrowHead(el3, ends, options) {
     var el = el3.node();
     var headStyle = ARROWPATHS[options.arrowhead || 0];
     var startHeadStyle = ARROWPATHS[options.startarrowhead || 0];
-    var scale = (options.arrowwidth || 1) * options.arrowsize;
-    var startScale = (options.arrowwidth || 1) * options.startarrowsize;
+    var scale = (options.arrowwidth || 1) * (options.arrowsize || 1);
+    var startScale = (options.arrowwidth || 1) * (options.startarrowsize || 1);
     var doStart = ends.indexOf('start') >= 0;
     var doEnd = ends.indexOf('end') >= 0;
     var backOff = headStyle.backoff * scale + options.standoff;