(fix) avoid exceptions for RRULE with no DTSTART

NEWS

@@ -20,6 +20,7 @@ Bug fixes
  - [core] honor IMAPLoginFieldName also when setting IMAP ACLs
  - [core] honor groups when setting IMAP ACLs
  - [core] honor "any authenticated user" when setting IMAP ACLs
+ - [core] avoid exceptions for RRULE with no DTSTART
 
 4.0.8 (2019-07-19)
 ------------------

SOPE/NGCards/iCalDailyRecurrenceCalculator.m

@@ -69,6 +69,10 @@
   dayMask = nil;
   repeatCount = 0;
 
+  if (!firstRange)
+    // Can happen when event/todo has a rrule with no dtstart
+    return nil;
+
   if ([endDate compare: firStart] == NSOrderedAscending)
     // Range ends before first occurrence
     return nil;

SOPE/NGCards/iCalWeeklyRecurrenceCalculator.m

@@ -79,6 +79,10 @@
   repeatCount = 0;
   hasRepeatCount = [rrule hasRepeatCount];
 
+  if (!firstRange)
+    // Can happen when event/todo has a rrule with no dtstart
+    return nil;
+
   if ([endDate compare: firStart] == NSOrderedAscending)
     // Range ends before first occurrence
     return nil;

SOPE/NGCards/iCalYearlyRecurrenceCalculator.m

@@ -59,7 +59,11 @@
   repeatCount = 0;
   count = 0;
   referenceDate = nil;
- 
+
+  if (!firstRange)
+    // Can happen when event/todo has a rrule with no dtstart
+    return nil;
+
   if ([rEnd compare: firStart] == NSOrderedAscending)
     // Range ends before first occurrence
     return nil;

SoObjects/Appointments/SOGoAppointmentFolder.m

@@ -1100,6 +1100,12 @@ firstInstanceCalendarDateRange: (NGCalendarDateRange *) fir
       endDate = [(iCalToDo*) component due];
     }
 
+  if (![master startDate])
+    {
+      [self errorWithFormat: @"ignored component with no DTSTART"];
+      return;
+    }
+
   delta = [masterEndDate timeIntervalSinceDate: [master startDate]];
   recurrenceIdRange = [NGCalendarDateRange calendarDateRangeWithStartDate: recurrenceId
 								  endDate: [recurrenceId dateByAddingYears:0 months:0 days:0 hours:0 minutes:0 seconds: delta]];