fix: simplify check for default_error404

[luisbg]

If sailor.conf.default_error404 is not defined, it is nil which will resolve to false with ~= ''. No need to check twice.

[luisbg]

Starting to read the flow of the code. From src/sailor.lua to conf, to controller, to view, to model.

:smile:

[Etiene]

Wait! It's supposed to get into the if only when there's a default error page. Nil is different from empty string and it would enter in the if, that's not the desired behavior, both checks are necessary... ^_^

[luisbg]

Oh! Sorry.

The code should check that it is not nil. I missunderstood the purpose of the check. My bad.

Closing the PR.

[Etiene]

no worries! :)