Code review comment for lp:~jjardon/indicator-datetime/fix-794312

I appreciate this patch, especially since the ticket was (incorrectly) closed as a duplicate of an unrelated ticket :) But, I don't think it addresses the OP's crash -- the retrace shows the final two steps were:

> g_type_check_instance_cast (type_instance=0x2849cb0, iface_type=42195904)
> ido_calendar_menu_item_set_date (menuitem=0x27d7440, year=2011, month=5, day=7) at idocalendarmenuitem.c:383

menuitem wasn't NULL in this trace, so guarding against NULL in the calling code probably won't help. In fact, ido_calendar_menu_item_set_date() is already safeguarding against NULL pointers in its first line that calls IDO_IS_CALENDAR_MENU_ITEM(). That's already null-safe -- but, unfortunately, not corrupt-pointer safe, which is why g_type_check_instance_cast() is crashing. ;)