#7 Email module sends to invalid addresses

[matt_t]

When using 'customer@gallery' in the 'e-mail address'
field of the checkoutemail configuration pane, and the
customer does not enter a valid e-mail address, the
Email.inc tries to send an email to an empty email
address: ' ', which gives an error.

The addresses used as destinations in any email should
be checked for valid format. This should also occur
in the admin page for the module.

[Nobody/Anonymous]

Logged In: NO

And -to be complete- if the customer enters no email
address at all (it's optional), no email should be sent to
the customer (which currently causes the error).