Bug 37643: Check for NaN instead of truthiness if calendar.inc accepts_time

Bug 37643: Check for NaN instead of truthiness if calendar.inc accepts_time

To test:
1) Go to circulation.pl (checking out to a patron)
2) Click the settings in the barcode input
3) Set any due date with the time set to 00:00
4) Note that the picker resets the time to 23:59
5) Apply the patch
6) Repeat 1-3
7) Note that the time (00:00) stays put
8) Sign off

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>