Fix connection error alerts when page unloads (#1488547)

CHANGELOG

@@ -1,6 +1,7 @@
 CHANGELOG Roundcube Webmail
 ===========================
 
+- Fix 'no connection' errors on page unloads (#1488547)
 - Plugin API: Add 'unauthenticated' hook (#1488138)
 - Show explicit error message when provided hostname is invalid (#1488550)
 - Fix wrong compose screen elements focus in IE9 (#1488541)

program/js/app.js

@@ -60,6 +60,8 @@ function rcube_webmail()
     beforeSend: function(xmlhttp){ xmlhttp.setRequestHeader('X-Roundcube-Request', ref.env.request_token); }
   });
 
+  $(window).bind('beforeunload', function() { rcmail.unload = true; });
+
   // set environment variable(s)
   this.set_env = function(p, value)
   {
@@ -6129,6 +6131,10 @@ function rcube_webmail()
     this.set_busy(false, null, lock);
     request.abort();
 
+    // don't display error message on page unload (#1488547)
+    if (this.unload)
+      return;
+
     if (request.status && errmsg)
       this.display_message(this.get_label('servererror') + ' (' + errmsg + ')', 'error');
     else if (status == 'timeout')