Improve display_message() for sophisticated 'loading' messages

So it's possible to display more than one message of type 'loading'
at a time and define custom timeout.

program/js/app.js

@@ -7906,6 +7906,14 @@ function rcube_webmail()
 
     if (!type)
       type = 'notice';
+    else if (type == 'loading') {
+      if (!key)
+        key = 'loading';
+      if (!timeout)
+        timeout = this.env.request_timeout * 1000;
+      if (!msg)
+        msg = this.get_label('loading');
+    }
 
     if (!key)
       key = this.html_identifier(msg);
@@ -7929,13 +7937,6 @@ function rcube_webmail()
       }
     }
 
-    if (type == 'loading') {
-      key = 'loading';
-      timeout = this.env.request_timeout * 1000;
-      if (!msg)
-        msg = this.get_label('loading');
-    }
-
     // The same message is already displayed
     if (this.messages[key]) {
       // replace label