[Pcr] Safe point

This safepoint may have existed prior to v38.1.

1. Open the attached file.
   Expected: SV appears.
2. Open the OP's "In Silico PCR" tab.
3. Set "AAAAAAAAAAAAAAA" as both primers.
4. Click "Find product(s) anyway".
   Expected: either the task runs without errors and outputs the correct answers, or an understandable error is displayed why the task cannot be completed.
   Current state: [Core Services][ERROR][] Trying to recover from error: Error: at least one primer should has a ledge on one side at C:\BuildAgent\work\release\ugene\src\plugins\pcr\src\InSilicoPcrTask.cpp:294