Removes [_1]..[_2] from fail_with() output

Fixes an issue with fail_with() subroutine when template uses line parameters for a string, but no key in %Lexicon is found:
Was:
<h1>[% c.l("Main [_1] Page [_1]",1,2) %]</h1> => Main [_1] Page [_1]
Is:
<h1>[% c.l("Main [_1] Page [_1]",1,2) %]</h1> => Main 1 Page 2