Crash when opening file if "Sanger Reads" is running

This issue relates to crash reports №№23949, 23950

Environment: Win10 x64, v. 38

The error appears every other time

Scenario

1. Open data/samples/ACE/BL060C3.ace as MSA
2. Close project, don't save
   These steps are required for BL060C3.ace to appear in the Recent Files
3. Click Tools->Sanger data analysis->Map reads to reference...
4. Set _common_data\sanger\reference.gb as reference
5. Add sanger_01.ab1–sanger_20.ab1 as reads
6. Click Map
7. While running Sanger, click BL060C3.ace from Recent Files on Start Page
8. Wait for the Sanger Reads Editor to appears
9. In Select Document Format dialog click OK
   Actual: sometimes crash