Crash when manipulating previous collection

[KatieWoe]

Test device
Dell
Operating System
Win 10
Browser
Chrome
Problem description
For phetsims/qa#459
When you manipulate atoms in a previous collection and return to the current one, graphical bugs result and a crash happens if you try to answer a question.
Steps to reproduce

1. Go to the first or second screen
2. Finish a collection
3. Go back to a previous collection and drag atoms out and around (may need to leave them out)
4. Go back to the current one.
5. Manipulate atoms
6. Try to answer problem

Visuals

Troubleshooting information:

!!!!! DO NOT EDIT !!!!!
Name: ‪Build a Molecule‬
URL: https://phet-dev.colorado.edu/html/build-a-molecule/0.0.0-dev.23/phet/build-a-molecule_all_phet.html?profiler
Version: 0.0.0-dev.23 2019-11-20 23:29:39 UTC
Features missing: touch
Flags: pixelRatioScaling
User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.97 Safari/537.36
Language: en-US
Window: 1536x722
Pixel Ratio: 2.5/1
WebGL: WebGL 1.0 (OpenGL ES 2.0 Chromium)
GLSL: WebGL GLSL ES 1.0 (OpenGL ES GLSL ES 1.0 Chromium)
Vendor: WebKit (WebKit WebGL)
Vertex: attribs: 16 varying: 30 uniform: 4096
Texture: size: 16384 imageUnits: 16 (vertex: 16, combined: 32)
Max viewport: 32767x32767
OES_texture_float: true
Dependencies JSON: {}

[Denz1994]

KitCollectionList.switchTo(collection) is being called when the yellow arrow buttons hit. This is a good place to start. Perhaps the kitPanel and kitPlayAreaNode should keep track of the current collection? Standby for more information.

[Denz1994]

This was fixed during #121 (comment). Closing this one.