Check if umbFileDropzone has queued items before showing ChooseMediaTypeDialog

The ChooseMediaTypeDialog is shown even if there are no queue items, for example due file errors. 
Checking the queue lenght in _requestChooseMediaTypeDialog prevents showing the dialog unnecessary.

src/Umbraco.Web.UI.Client/src/common/directives/components/upload/umbfiledropzone.directive.js

@@ -187,6 +187,11 @@ angular.module("umbraco.directives")
 
                     function _requestChooseMediaTypeDialog() {
 
+                        if (scope.queue.length === 0) {
+                            // if queue has no items so there is nothing to choose a type for
+                            return false;
+                        }
+                        
                         if (scope.acceptedMediatypes.length === 1) {
                             // if only one accepted type, then we wont ask to choose.
                             return false;