The "Select Subalignment" dialog can be shown twice when exporting subalignment as image

Affected tests:

• GUITest_common_scenarios_msa_editor_test_0045
• GUITest_regression_scenarios_test_2951
• GUITest_common_scenarios_workflow_scripting_test_0003

Scenario:

1. Open "COI.aln".
2. In the context menu in the sequence area select "Export->Export as image".
3. In the "Export Image" dialog set "Region" to "Custom region". Click the "Select" button nearby.
   Expected state: the "Select Subalignment" dialog appears.
4. Click the "Cancel" button in the dialog.
   Expected state: the "Select Subalignment" dialog is closed.
   Actual state: the dialog is closed and opened again immediately.

A similar problem appears when selecting value in "user script" combobox in the WD.