Crash in g_date_time_to_instant()

Random crash when I wasn't using Clocks (it must have been running as a background service). Please see the downstream bug attachment for a full quality backtrace. Truncated backtrace:

Truncated backtrace:
Thread no. 1 (4 frames)
 #0 g_date_time_to_instant at ../glib/gdatetime.c:2709
 #1 g_date_time_to_timezone at ../glib/gdatetime.c:2709
 #2 clocks_world_item_calculate_riseset at src/25a6634
 #3 clocks_world_item_real_tick at src/25a6634

Downstream: https://bugzilla.redhat.com/show_bug.cgi?id=1819367