Remove some index -1 exceptions

[RolandPheasant]

1. Prevent index -1 exception when connecting to source list. Fixes [Bug]: AddRange ChangeSet has unexpected Index of -1 #723
2. Prevent further index=-1 exceptions when converting an observable collection (including AvaloniaDictionary). Fixes [Bug]: System.ArgumentException: index cannot be greater than the size of the collection #683 and fixes [Bug]: System.ArgumentException: index cannot be negative #710

[RolandPheasant]

@JakenVeina

I will say you should add a comment here, mentioning that this is copied directly form Avalonia, and why.

I actually thought that but didn't bother. You're right. Comment added and pushed.

[RolandPheasant]

@JakenVeina

UnspecifiedIndexException?

Ouch, Good call. I'd forgotten this was even a thing, It's been so many years. I'll consolidate

[JakenVeina]

@RolandPheasant

Ouch, Good call. I'd forgotten this was even a thing, It's been so many years. I'll consolidate

Yeah, that's definitely what I was referring to. Not just attempting to suggest a different name that I didn't think already existed.

[github-actions]

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