make code more safe (RT#79458)

In _style, there is:

      my @c = ref($code) eq 'ARRAY' ? @$code : $code if $code;

This is unsafe. "my <var> ... if <condition>" has undefined behaviour in
the case of <condition> being false.

From perlsyn:

NOTE: The behaviour of a "my" statement modified with a statement
modifier conditional or loop construct (e.g. "my $x if ...") is
undefined.  The value of the "my" variable may be "undef", any
previously assigned value, or possibly anything else.  Don't rely on
it.  Future versions of perl might do something different from the
version of perl you try it out on.  Here be dragons.