Problem: Calling `vim.filetype.match({ filename = '...', buf = ... })`
during startup results in an error due to not yet defined
`g:ft_ignore_pat`.
Solution: Add a guard to check `g:ft_ignore_pat` related properties only
if the variable is defined. This also allows to simplify other tests
which did not depend on `g:ft_ignore_pat` but required it explicitly
set to work.
6b9b4a1377
