Return trips on December 31, 1899

[werebus]

Our admincoord, emailed that she had noticed a number of requests where the return-trip pickup date and time was some time on December 31, 1899.

I don't know the cause of this, but some things to note.

• In looking through the logs, it was several different users
• but always the same field (field_25)
• The date was always 1899-12-31, but the time was different (13:15, 16:00, 16:00, 14:00, 15:00)

@dfaulken found xdan/datetimepicker#436, but I'm having trouble reproducing the behavior reported there.