Check if umbFileDropzone has queued items before showing ChooseMediaT…

…ypeDialog

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;