avoid crash when __FILE__ is used at top level (bug #44363) * lex.ll (octave_base_lexer::is_keyword_token): Call correct constructor for magic_file_kw. * token.h, token.cc (token::token (int, const char *, int, int)): New constructor.

%!function r = f (x)
%!  if (ischar (x))
%!    r = x;
%!  else
%!    error ("expecting character string");
%!  endif
%!endfunction

%!assert (eval ("f 10;"), "10");