JT-21431: Actions with groups: gray screen and spoiled database

STR:

1. Create 3 or 4 groups (or not, if you already have them) - let them be g1, g2, g3
   
2. Merge g1 with g2
   
3. g1 will disappear in some seconds. In a time it is not yet disappeared, click on merge
   
4. In the opened dialog merge g2 with g3; confirmation alert in the browser will appear 2 times
   
5. Wait for a second and understand that you haven't got root access anymore.

Moreover, there is nobody who has root access now. Actually, now you can delete your database because nobody can access it.
groups1.jpg represents what you see after step 5 and before refresh, groups2.jpg - after refresh

Another STR:

1. Create 3 or 4 groups (or not, if you already have them) - let them be g1, g2, g3
   
2. Merge g1 with g2
   
3. g1 will disappear in some seconds. While it is not yet disappeared, click on diff (group does not matter)
   
4. Diff some groups, then close the window.

Window stays gray, as you can see in groups3.png