MISSING_SUBJECT not triggered if subject contains whitespace

[Sebastian Arcus]

I've had a number of emails with no subject not triggering the 
MISSING_SUBJECT rule - only to discover that the spammers have added a 
white space after 'Subject:' - which appears to fool the code into 
thinking that there is an actual subject. Would it be possible to 
'smarten up' the code a bit to recognise this?