[perl #114456] [BUG] Invocation '()' after sub declaration doesn't parse in Rakudo (but does in STD)

[Christian Bartolomaeus via RT]

This works now:

$ perl6-m -e 'say sub { 5 }()'
5

$ perl6-m -e 'sub ($t) { say $t }("arf")'
arf

I added tests to S02-lexical-conventions/sub-block-parsing.t with the following 
commit: https://github.com/perl6/roast/commit/09ff5366a3