gnulib/regcomp: Fix resource leak

gnulib/regcomp: Fix resource leak

In the functions create_initial_state() and calc_eclosure_iter(), memory
is allocated for the elems member of a re_node_set structure but that
memory isn't freed on error. Before returning an error, a call to
re_node_set_free() should be made to prevent the resource leak.

This issue has been fixed in the latest version of gnulib and I've
backported this change to maintain consistency.

This issue was found by a Coverity scan of GRUB2 under the following
CIDs: 473869, 473888.

Fixes: CID 473869
Fixes: CID 473888
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>