Vendor Invoice bug in 1.2.X

[Luke <..hidden..>]

Not sure if this is fixed in versions of 1.2 beyond 1.2.18, but:

If a vendor invoice is posted without a duedate, the following happens:

DBD::Pg::st execute failed: ERROR: invalid input syntax for type date: ""

I think the due date should be generated in the same way it is for 
customers on sales invoices.

I have not tested setting actual terms (or days at least) on a vendor, to 
see if that makes a difference, but 0 days should be assumed, and a same 
day date generated.

Luke