Regression: SAFE_POINT if select "Trim left end" from context menu in Sanger editor

Issue is not reproducible on 39.0 release
Scenario:
Open UGENE with clean ini file
1. Open _common_data/sanger/alignment.ugenergb
Expected: Chromatograms and overview are present on the screen.
2. Select first sequence name in the name list
3. Select context menu Edit->Trim left end
SAFE_POINT occurs:

Trying to recover from error: Failed to insert gaps into an alignment! at D:\ugene\ugene\src\corelibs\U2Core\src\gobjects\MultipleAlignmentObject.cpp:437
Assertion failed: 0, file D:\ugene\ugene\src\corelibs\U2Core\src\gobjects\MultipleAlignmentObject.cpp, line 437

Expected: Menu item should not be enabled if selected only sequence name

Another scenario:
1. Select first sequence name in the name list
2. Select context menu Edit->Remove character/gap
Actual: Sequence line is removed
Expected: Menu item should not be enabled if selected only sequence name