Fix `_hideDetailViewController` not being reset properly

[nicoco007]

_hideDetailViewController doesn't get reset properly in LevelCollectionNavigationController.DidActivate and causes a race condition that doesn't dismiss view controllers properly on the level end screen if:

1. a song is automatically selected by BSL when coming from the main menu
2. the active tab is a non-level-pack tab (i.e. favorites or all songs)
3. a view controller is presented on the level end screen's right pane (e.g. by BeatSaviorData)

This causes ClearChildViewControllers to be called too early and eventually HMUI.Screen.SetRootViewController gets called twice in a row for the same screen, which in turn causes TransitionCoroutine to be cancelled so the previous view controller (i.e. the leaderboard) is never dismissed/disabled.

Basically, this is a fix for this issue:

[kinsi55]

Based off a 1 minute decompiler check, am I assuming correctly that the fix would also work properly if you only set it to false if addedToHierarchy is true?

[nicoco007]

Maybe, but since the issue is related to ClearChildViewControllers, the else if (_loading) might also come into play at some point. ClearChildViewControllers is eventually called by all code paths so I thought it'd be simpler to just set it to false no matter what.

[kinsi55]

I see, well its more or less essentially a basegame issue (Since I use basegame logic to set the start state) so please report to devs 👍