Impossible to delete first symbol in one-lined alignment

It is regression.

Scenario:

1. Open _common_data/scenarios/msa/ma_one_line.aln.
2. Set the cursor at the beginning of the line.
3. Select the first symbol "T".
4. Click "Delete".
   Expected state: Symbol is deleted
   Actual state: Nothing happens

Affected tests:
GUITest_regression_scenarios_test_2030