[perl #63568] Null PMC access when calling .arity on a multi sub in Rakudo

[Carl Mäsak via RT]

Also .signature on multis:

<szabgab> rakudo: sub f($z) {}; &f.signature.perl.say
<p6eval> rakudo af4b73: OUTPUT«:(Any $z)␤»
<szabgab> rakudo: multi sub f($z) {}; &f.signature.perl.say
<p6eval> rakudo af4b73: OUTPUT«Null PMC access in find_method() [...]