(js) Fix handling of attachments in mail editor

Fixes #4058, #4063

UI/WebServerResources/js/Mailer/Mailbox.service.js

@@ -157,7 +157,7 @@
    */
   Mailbox.prototype.init = function(data) {
     var _this = this;
-    if (data.headers) {
+    if (angular.isUndefined(this.uidsMap) || data.headers) {
       this.$isLoading = true;
       this.$messages = [];
       this.uidsMap = {};

UI/WebServerResources/js/Mailer/Message.service.js

@@ -474,9 +474,9 @@
    * @param {string} filename - the filename of the attachment to delete
    */
   Message.prototype.$deleteAttachment = function(filename) {
-    var action = 'deleteAttachment?filename=' + filename;
+    var data = { 'filename': filename };
     var _this = this;
-    Message.$$resource.post(this.$absolutePath({asDraft: true}), action).then(function(data) {
+    Message.$$resource.fetch(this.$absolutePath({asDraft: true}), 'deleteAttachment', data).then(function(data) {
       Message.$timeout(function() {
         _this.editable.attachmentAttrs = _.filter(_this.editable.attachmentAttrs, function(attachment) {
           return attachment.filename != filename;