Pattern Generator: Group crush

[IonutMuthi]

Environment:

• OS: Windows
• FW Version
• SW v2.0.0-beta-rc2-a3a7c43

Describe the bug
After creating a group and starting to create another group you are able to select the already grouped channels and then pressing "x" button in the menu for one of them causes Scopy to crash

To Reproduce
Steps to reproduce the behavior:

1. Go to Pattern Generator
2. group 0 and 1
3. press done
4. press group again
5. select 0 and 1
6. press x on any of them
7. Scopy will crash

Expected behavior
The channels that are in one group can't be added in another