addresses RM7710 but needs review, esp on db.rb

This commit attempts to address https://dev.metasploit.com/redmine/issues/7710 which might 
be poorly written, but 7710 is a spinoff of https://dev.metasploit.com/redmine/issues/7269 to 
give you some background

egypt, you really need to review this, or someone else.  I'm not sure
they're all needed (all the checks for nil/empty).  I didn't see good places to add checks in the
parser files themselves, most of the changes to parser files in this PR are cosmetic.

The meat of the commit is in db.rb and that needs a good review.