Fix thinko in toke.c in 211a434

Oops.  We can’t fiddle with the rv2cv op’s GV kid if it actually a
padcv op.  Don’t even look at it when handling a lexical sub call,
because we don’t need it anyway.

This should hopefully mitigate valgrind complaints.
Add test for \p{} failing silently

This tests the fix added in commit 2db3e09128.

Only after writing what I said in
<20140901194542.21940.qmail@lists-nntp.develooper.com> did I realise
that this is actually trivial to test.