Add a more helpful crash on missing frames

[PunkPun]

Currently it crashes with: exception of type System.IndexOutOfRangeException: Index was outside the bounds of the array.

With no hint to where the issue resides
This is hot code though it runs only once on game / map start

[anvilvapre]

untested.

[abcdefg30]

From @pchote on Discord:

https://github.com/OpenRA/OpenRA/blob/bleed/OpenRA.Mods.Common/Graphics/DefaultSpriteSequence.cs#L544 is where it is supposed to be handled
i suspect we should be ignoring out of index frames in the cache and then letting that line throw the error
or have some other mechanism for SpriteCache to allow the SpriteSequence to do validation and throw

Would be checking if resolved[f] is in bounds work here?

OpenRA/OpenRA.Mods.Common/Graphics/DefaultSpriteSequence.cs

Line 495 in 10d7436

resolved = r.Frames.Select(f => resolved[f]).ToArray();

And then just if (i >= loadedFrames.Length) continue; in the loop in SpriteCache.

This would have the advantage of being able to report {image}.{Name} in the exception.

[PunkPun]

That doesn't catch all errors. For example setting an invalid ShadowStart still crashes with out of index, just in a different place