Panic when preparing route statuses

[sjberman]

Describe the bug
Sometimes there can be a panic when building the route statuses by accessing an index out of range. I believe it occurs when a Route is configured without a sectionName, referencing a Gateway with a single listener. I also had multiple different Gateway API implementations deployed, so that could play a role in this as well.

The code basically attempts to do some de-duplication of shared indices of ParentRefs in this scenario, but accesses an index that doesn't exist.