MacOS 13: EKSource sometimes has nil title

MacOS 13 sometimes returns nil for non-iCloud source
titles. Provide a dummy source title instead.

Author: sfsam

Itsycal/EventCenter.m

@@ -193,16 +193,20 @@ - (void)_fetchSourcesAndCalendars {
     NSMutableArray *sourcesAndCalendars = [NSMutableArray new];
     NSString *currentSourceTitle = @"";
     for (EKCalendar *calendar in calendars) {
+        NSString *calendarSourceTitle = calendar.source.title;
+        // (!) Should never hit this case, but MacOS 13 sometimes returns
+        // nil for non-iCloud source titles. Use a dummy title instead.
+        if (!calendar.source.title) calendarSourceTitle = @"???";
         if (!calendar.color) {
             // Skip calendars where the color is nil.
             // This normally doesn't happen, but there are some
             // edge cases where it does.
             // See: github.com/sfsam/Itsycal/issues/152
             continue;
         }
-        if (![calendar.source.title isEqualToString:currentSourceTitle]) {
-            [sourcesAndCalendars addObject:calendar.source.title];
-            currentSourceTitle = calendar.source.title;
+        if (![calendarSourceTitle isEqualToString:currentSourceTitle]) {
+            [sourcesAndCalendars addObject:calendarSourceTitle];
+            currentSourceTitle = calendarSourceTitle;
         }
         CalendarInfo *calInfo = [CalendarInfo new];
         calInfo.calendar = calendar;

Itsycal/EventViewController.m

@@ -269,7 +269,8 @@ - (void)viewWillAppear
                     [_calPopup.menu addItem:[NSMenuItem separatorItem]];
                 }
                 NSMenuItem *sourceItem = [NSMenuItem new];
-                sourceItem.title   = calInfo.calendar.source.title;
+                // MacOS 13 sometimes returns nil for non-iCloud source titles.
+                sourceItem.title   = calInfo.calendar.source.title ?: @"???";
                 sourceItem.enabled = NO;
                 [_calPopup.menu addItem:sourceItem];
                 currentSource = calInfo.calendar.source;