edit-dialog: set minimum number of occurrence to 2

An event should be considered as recurring only when it occurs
at least 2 times.

So to make sure the number of occurrences are at least 2,
set minimum value of recurrence spin button as 2.

https://bugzilla.gnome.org/show_bug.cgi?id=787054

src/gcal-edit-dialog.c

@@ -1261,7 +1261,7 @@ gcal_edit_dialog_set_event (GcalEditDialog *dialog,
 
   dialog->setting_event = TRUE;
 
-  count_adjustment = gtk_adjustment_new (0, 1, G_MAXDOUBLE, 1, 1, 10);
+  count_adjustment = gtk_adjustment_new (0, 2, G_MAXDOUBLE, 1, 1, 10);
 
   gtk_spin_button_set_adjustment (GTK_SPIN_BUTTON (dialog->number_of_occurrences_spin), count_adjustment);