Maintainer email can be left blank if not touched and other tabs active when saved.

[raintonr]

This is probably a bug in admin....

When performing config, the 'Challenges' tab opens first for whatever reason. By default 'Maintainer email passed to CA' on the 'Main' tab is blank. If one does not actually open the 'Main' tab though, config can be saved despite the email being blank as it's validator function doesn't seem to be called.