datetime: Fix segfault on exit
datetime: Fix segfault on exit

We have to check the ev->type in the handler otherwise we will attempt
to modify state when we get the GP_WIDGET_FREE event.

Signed-off-by: Cyril Hrubis <b1e90efd3b808b8e0bcf2a9a55fd8b9a779bfd81@ucw.cz>

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