Fix for reading certain CRN textures

[lilleyse]

Reported on the forum: https://groups.google.com/forum/#!topic/cesium-dev/0Io8gRRHIgs

In some cases dxtData will exceed length which throws an exception with set. This creates a view of the exact size needed before the set call.

[bagnell]

dxtData will exceed length when there are mimaps. Perhaps add a comment?

Update CHANGES.md.

[lilleyse]

Updated

[bagnell]

Also, can you add a test?

[bagnell]

Like we discussed offline, loading KTX has the same problem.

[lilleyse]

Updated.

For KTX I just replaced .slice with new Uint8Array. Is the deep copy in transcodeCRNToDXT there because it's in a web worker?

[bagnell]

Is the deep copy in transcodeCRNToDXT there because it's in a web worker?

Yes. We need to transfer the buffer back to the main thread; otherwise, we would need to transfer the whole buffer used by the transcoder.