[3.x] Silence Index track = N is out of bounds error when deleting the last animation track

[error-27]

Instead the method silently returns when the index is out of bounds.

• Fixes Godot 3.5: AnimationPlayer Animation window: deleting last track causes spurious error "Index track = N is out of bounds (animation->get_track_count() = N)" #79587

[TokageItLab]

It is very easy to hide errors, but it is generally a bad fix. The errors in core are basically there because they should be checked, so you need to look for the more fundamental problem first.

Since the issue #79587 is that the error occurs after the track is deleted, I guess the problem is with the timing of the update of the track count in the function involved in deleting the track.

[error-27]

It's been a few weeks and I'm just going to close this now. I exhausted what leads I had, I have no prior experience with this code, and I don't have the time anymore to keep investigating. Perhaps someone else will fix it, or I'll come back if this is still an issue later on.