Fix for  'portagegt': can't convert nil into String

This fixes a case where someone (like me :) might not have defined a category, but still there is no warning in the log unless there was a optFlag. I suppose optFlag are portage specific things, as I noticed this error on packages where I specified things like require =>.
Which breaks the bank with the following message:

    err: Could not prefetch package provider 'portagegt': can't convert nil into String