Arend Errors: line number is not updated after some modifications in the editor

[marat-rkh]

Steps:

1. Have some declaration with a goal.
2. Open Arend Errors and check the line number (3 in this case).
3. Add a new line before the declaration.

Expected: the line number in Arend Errors becomes 4. Actual: it remains 3 and changes only when I click on it.