- Fix: Map extension click events to "mousedown" so they can be received

on touch devices (since `touch.js` changes `touchstart` to
    `mousedown`) (@ClemArt); closes #168
- Fix: Ensure extension `mouseup` events run on "zoom" and "select"
  modes (@iuyiuy); closes #159

editor/svgcanvas.js

@@ -2615,7 +2615,7 @@ const mouseUp = function (evt) {
         }
       }
     }
-    return;
+    break;
   case 'zoom':
     if (rubberBox != null) {
       rubberBox.setAttribute('display', 'none');
@@ -2628,7 +2628,7 @@ const mouseUp = function (evt) {
       height: Math.abs(realY - rStartY),
       factor
     });
-    return;
+    break;
   case 'fhpath':
     // Check that the path contains at least 2 points; a degenerate one-point path
     // causes problems.