Fix support for recurrent tasks

SoObjects/Appointments/iCalToDo+SOGo.m

@@ -1,6 +1,6 @@
 /* iCalToDot+SOGo.m - this file is part of SOGo
  *
- * Copyright (C) 2008-2014 Inverse inc.
+ * Copyright (C) 2008-2017 Inverse inc.
  *
  * This file is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -188,7 +188,11 @@
 
 - (NSTimeInterval) occurenceInterval
 {
-  return [[self due] timeIntervalSinceDate: [self startDate]];
+  if ([self due])
+    return [[self due] timeIntervalSinceDate: [self startDate]];
+  else
+    // When no due date is defined, base recurrence calculation on a 60-minute duration
+    return 3600;
 }
 
 @end