Uninformative error message in "Export subaligment" dialog for incorrect file name

Affected test:   *GUITest_common_scenarios_msa_editor_test_0062*

The issue began to appear after editing the bug UGENE-6624.
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Scenario:+

1. Open COI.aln.
2. Select "Export->Save subalignment" from context menu.
   Expected result: "Extract selected as MSA" dialog appears
3. Set any path to the directory in "File name" field, for example "data\samples\CLUSTALW\"
4. Click "Extract" button
   Expected result: "Filename to save is empty" message in the message box
5. Open the same dialog once more and set "File name" to "data\samples\CLUSTALW" without last slash
6. Click "Extract" button
   Actual result: ** Error message

ERRROR:'Create sub-alignment and open view: COI.aln' task failed: Subtask {Create sub-alignment: COI.aln} is failed: Subtask {Save document} is failed: Failed to detect IO adapter for D:/ugene/ugene/data/samples/CLUSTALW