Fix the wrong order of the boundary rectangles in TileAvailability

[baothientran]

When rectangles are inserted into the QuadtreeNode in TileAvailability, they are ordered by level using the index returned by binarySearch(). However, it negates the index when it is 0, which results in the wrong order of the rectangle lists and wrongly identify a tile is not available. This is the Sandcastle example

Below is the visual problem:

Before the fix. The tile is not really detail because it is falsely identified as unavailable and therefore, upsampled from the parent

After the fix. It is much more detail now

@lilleyse Can you please take a look at it? Please let me know if I should add anything

[cesium-concierge]

Thanks for the pull request @baothientran!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.
• ❔ Unit tests were not updated.
  • Make sure you've updated tests to reflect your changes, added tests for any new code, and ran the code coverage tool.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[lilleyse]

@kring can you review?

[mramato]

I'll be that guy and ask if there is an easy way to add a unit test for this? Only if it doesn't require a massive amount of hoop-jumping.

[baothientran]

@mramato I think the error can be replicated with a simple unit test. I will add it right away

[baothientran]

I think this is ready for review

[lilleyse]

@baothientran can you update CHANGES.md?

[kring]

Thanks @baothientran, great catch!