_solve_..slot_conflicts: fix bug #522084

Fix _solve_non_slot_operator_slot_conflicts to add all parents to the
conflict_graph, even for parents where the atom matches all relevant
nodes. Otherwise, we risk removing all of the matched nodes from the
graph, which would cause a missed update.

X-Gentoo-Bug: 522084
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=522084