Stop / $looks_like_block/ from leaking

Stop / $looks_like_block/ from leaking

If an interpolated string looks as though it contains a regexp code
block, the regexp compiler will evaluate it inside qr'...' and then
extract the code blocks from the resulting regexp object.

If it turned out to be a false positive (e.g., "[(?{})]"), then
the code to handle this returned without freeing the temporary reg-
exp object.