clock: Don't assume that the month cannot be 0
The month
property can be between 0 and 11, so the value 0 is valid.
This fixes the problem that gnome-panel throws the following messages when I open the month January in the calendar:
** (gnome-panel:6772): CRITICAL **: 21:38:42.043: calendar_client_get_events: assertion 'client->priv->month != 0' failed
** (gnome-panel:6772): CRITICAL **: 21:38:42.043: calendar_client_foreach_appointment_day: assertion 'client->priv->month != 0' failed
** (gnome-panel:6772): CRITICAL **: 21:38:42.043: calendar_client_get_events: assertion 'client->priv->month != 0' failed
** (gnome-panel:6772): CRITICAL **: 21:38:42.049: calendar_client_get_events: assertion 'client->priv->month != 0' failed
It seems that it's caused by this commit: 6902d889