[perl #120561] [BUG] use lib "double-quoted string" Null PMC

[Christian Bartolomaeus via RT]

There is still a Null PMC access on Parrot. The command runs fine on Moar and 
JVM:

$ perl6-p -e 'use lib "{$?FILE.path.directory}/lib";'
===SORRY!===
Null PMC access in get_bool()

I added a test (fudged 'skip' for Parrot) to S10-packages/basic.t with commit 
https://github.com/perl6/roast/commit/babf7685de