fix for WoW SoD MouseFocus -> MouseFoci

[hexagon5un]

A recent SoD version broke ItemRack by changing a function GetMouseFocus() to GetMouseFoci(), which returns an array instead of a single value.

This patch implements a quick fix that I got on the Simonize rogue discord: https://discord.com/channels/808033004797952021/808070665177399316/1288822112173166676

I'm just pushing it forward. :)

[Rottenbeer]

Does this also work in Classic non SoD, and Cata?

[hexagon5un]

Sorry, I don't know. I've been using this version in SoD, and it has worked great up to now. This makes it continue to do so.

I just noticed that someone is maintaining a SoD-specific fork, so if nobody else on SoD is using this one, you can delete my pull request. My guess is that SoD people who started recently will be using that one anyway.

[romracer]

The SoD one is mine but it exists mostly because PRs here were stale for awhile. At this point it's probably not much different than this one, though Styx sent me a PM to help confirm that - which I'll try to do this weekend.

But to this PR specifically, @hexagon5un have you tried V4.21? This was supposedly fixed in #270 which is included in the latest versions.

[Rottenbeer]

@romracer I'd be interested in a fox that works on classic and sod then everyone that installed the addon gets it.
I was kinda busy with work, that's why I didn't merge much, but it's fine now.
Maybe you can drop me a email if you want to contribute further?