[Exim] quota_warn_threshold

A very minor suggestion. exim currently panics if you set
quota_warn_threshold to a percentage (say 90%) without setting quota_warn
for every delivery.

Can I suggest it might be a little more forgiving, and ignore
quota_warn_threshold if quota is not set? This would make configs simpler in
the case where the quota is being looked up in a database, but not everyone
has a quota.

e.g. what I'd like is:

quota = ${if match {${extract{p3}{LDAP_EXPR}}}{([0-9]+)S}{$1}{}}
quota_warn_threshold = 90%

but at the moment actually I have to do:

quota = ${if match {${extract{p3}{LDAP_EXPR}}}{([0-9]+)S}{$1}{}}
quota_warn_threshold = ${if match {${extract{p3}{LDAP_EXPR}}}{([0-9]+)S}{90%}{}}

:-)

Regards,

Brian.