Avoid binding events in duplicate

This is particularly important as a resize event will trigger a call to this
(via resize -> _init() -> set() -> image load -> image load -> bindEvents())
and the 'hover' event type also triggers a 'mouseover' event having added an
event listener for the same. This all means that each time a browser sends a
resize event (which can happen on other events than a viewport width/height
change) more event listeners are stacked, leading to significant CPU usage for
no value.

Author: fredden

lib/web/magnifier/magnifier.js

@@ -401,6 +401,13 @@
         }
 
         function bindEvents(eType, thumb) {
+            var eventFlag = 'hasBoundEvent_' + eType;
+            if (thumb[eventFlag]) {
+                // Events are already bound, no need to bind in duplicate
+                return;
+            }
+            thumb[eventFlag] = true;
+
             switch (eType) {
                 case 'hover':
                     hoverEvents(thumb);