time_picker: Set minutes to zero in global time picker.

Usually when a user uses the time picker, they're most likely going to
set the time to the hour rather than the current minute. These changes
will set the minutes to zero whenever we are opening the global time
picker.

Fixes: #23874.

web/src/timerender.ts

@@ -355,9 +355,10 @@ export function get_timestamp_for_flatpickr(timestring: string): Date {
         // we use it to initialize the flatpickr instance.
         timestamp = parseISO(timestring);
     } finally {
-        // Otherwise, default to showing the current time.
+        // Otherwise, default to showing the current time to the hour.
         if (!timestamp || !isValid(timestamp)) {
             timestamp = new Date();
+            timestamp.setMinutes(0, 0);
         }
     }
     return timestamp;