gluon-status-page: don't reset signal graphs on resize events if width hasn't changed

Mobile browsers will often show or hide the address bar while scrolling.
This causes resize events which would often reset the signal graphs.

Fixes #662

package/gluon-status-page/src/js/lib/gui/signalgraph.js

@@ -110,7 +110,7 @@ define(function () {
     function resize() {
       var newWidth = canvas.parentNode.clientWidth
 
-      if (newWidth === 0)
+      if (newWidth === 0 || newWidth === canvas.width)
         return
 
       var lastImage = ctx.getImageData(0, 0, newWidth, canvas.height)