Effective role screen should be read only

[imorenov94]

Environment

• Platform version: 7.2.15
• Database: PostgreSQL
• Operating system: Windows

Description of the bug or enhancement

Steps to reproduce:

1. Run CUBA app
2. Navigate to Administration-> Users-> Invoke context menu -> Show effective role
3. Invoke context menu for any item -> Allow -> Click cancel button->Save

ER: As was mention in the forum question need either disable context menu actions or doesn't show dialog after cancel
AR: Has been getting the exception