[perl #115294] [BUG] Null PMC access when using variable in interpolated block in double-quoted string in regex in Rakudo

[Christian Bartolomaeus via RT]

This looks good now: It doesn't die anymore, but returns "foo bar".

$ perl6-m -e '$_ = "foo bar"; say m/ "{ $_ }" /'
｢foo bar｣

$ perl6-p -e '$_ = "foo bar"; say m/ "{ $_ }" /'
｢foo bar｣

$ perl6-j -e '$_ = "foo bar"; say m/ "{ $_ }" /'
｢foo bar｣

I added a test to S05-mass/rx.t with the following commit: 
https://github.com/perl6/roast/commit/98ef6a0163