…s with quantifiers

When a branch inside an alternation has a + or * quantifier, the
quantifier's pass_through step loops back to the branch's first step.
The alternation linking also sets that step's alternative_index to
point to the next branch. This causes the quantifier loop-back to
incorrectly explore other branches in the case of a failed match that
follows a successful match, contaminating captures.

This is corrected by redirecting the quantifier loop-back to a
"clean" copy of the target step without the alternative index pointing
to the next alternation branch.

Co-authored-by: Riley Bruins <ribru17@hotmail.com>
(cherry picked from commit 596a4d6)