Currently, the hour component of the time is doubled when switching from
AM to PM, which is incorrect. This commit fixes the logic by adding 12
hours when switching to PM.
https://bugzilla.gnome.org/show_bug.cgi?id=765370
If GcalEditDialog.format_24h is initialized to zero, the call to
gcal_edit_dialog_set_time_format() from GcalWindow will not make
period_combo boxes visible on systems, where 12-hour clocks are used.
This commit fixes that by removing the if statement from the function.
https://bugzilla.gnome.org/show_bug.cgi?id=765370
Ernestas Kulik