GUAC-978 use $evalAsync instead of $apply to avoid digest in progress error.

guacamole/src/main/webapp/app/client/directives/guacClient.js

@@ -353,7 +353,7 @@ angular.module('client').directive('guacClient', [function guacClient() {
 
                 }
 
-                $scope.$apply(updateDisplayScale);
+                $scope.$evalAsync(updateDisplayScale);
 
             });