Occasional сrash in sl_updateRealignAction

This crashthis happens about once every 5 releases: 50.0, 45.0, 40.0, 35.1.
2 possible invalidation options:

1. Global UGENE problem: lack of disk memory. Most likely this happened in the UCR-2562, resulting in a crash. This is a global, but minor, epic for the exploration of all such potentially dangerous places.
2. All other problems are similar in that at some point the internal alignment invariants broke due to something. If we take into account the last 2 similar crashes 2840 (this one) and 1135, then in both cases, users deleted sequences from the alignment, and then restored them using Ctrl+Z (cancel deletion of a sequence = adding, inserting a sequence). However, re-insertion was unsuccessful. The reasons for incorrect sequence insertion are unclear.

The crash occurs because, after an incorrect insertion, the cached alignment became null in MsaObject.cpp:930. Adding a check for null is difficult: if it was not possible to load/update the alignment, then what to do next?