[BUG] Crash when changing color-types

[bryanjclark]

• I have read through CONTRIBUTING.md

Describe the bug
In the color editor, if you have the cursor in the hex-color field, and tap a different color-representation type, the app crashes on TweakColorEditViewController:190.

To Reproduce
Steps to reproduce the behavior:

1. Go to the color-editor and tap on the hex-code field.
2. Tap on the RGBa segmented control.
3. App crashes.

Expected behavior
You should switch to RGBa editing mode no problem.

Desktop (please complete the following information):

• OS: iOS 14
• Device: iOS Simulator