[perl #93982] [BUG] Errors from typed variable declaration with missing initializers

[Christian Bartolomaeus via RT]

This works now (probably for quite a while already):

> my Str ($a) = ();
(Str)

I added a test to S02-types/type.t with this commit: 
https://github.com/perl6/roast/commit/b93b78792bcd5a0fef75bd2676ed1eac3e330562