Make zip code field optional on registration/register (#2358)
Make zip code field optional on registration/register (#2358)

* Make zip code field optional on registration/register
Fixes https://github.com/magfest/ubersystem/issues/2259.

* Make zip field optional in at-or-post-con mode

This matches the logic we use for checking this field in the back-end.

magfest/ubersystem,md1024/rams,magfest/ubersystem,RAMSProject/rams,magfest/ubersystem,md1024/rams,magfest/ubersystem,md1024/rams,RAMSProject/rams,RAMSProject/rams