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>
(cherry picked from commit e96a334aa8)
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>

koha-tmpl/intranet-tmpl/prog/en/includes/calendar.inc

@@ -116,7 +116,7 @@
             if ( !accepts_period ) {
                 if ( accepts_time ) {
                     let parsedDate = flatpickr.parseDate(dateText, instance.config.dateFormat);
-                    if ( !parsedDate.getHours() ) {
+                    if ( Number.isNaN(parsedDate.getHours()) ) {
                         instance.setDate(selectedDates[0].setHours(23, 59, 0, 0));
                     }
                 }