O01eg

> MacOS 10.15 also would be removed by Github by August 30... It could affect SDK builds.

Log contains multiple line like: ``` 16:37:33.885671 {0x00007f3aa0cee040} [error] client : ClientUI.cpp:1099 : Unable to load texture "/mnt/new/o01eg/build-freeorion-master-dedicated/default/data/art/stars/blackhole3.png.import" reason: Texture file "/mnt/new/o01eg/build-freeorion-master-dedicated/default/data/art/stars/blackhole3.png.import" does not have a supported file extension 16:37:33.885700...

`.import` files could be cleaned as they aren't part of repository as workaround.

@Zireael07 Godot generates them so I though it's a generated files.

@MichaelCourtney I've published them here https://freeorion-test.dedyn.io/FO0020-saves.7z

@geoffthemedio I'm not yet tested code with sanitizers.

> The clean solution is to initialise the invariants after all parsing is finished. I suppose we can use `Pending::WaitForPending` before initialize the invariants.

Yes, in `IApp::StartBackgroundParsing` values ref should be moved last, also each Pending should be saved in variables and each variables should be waited before values ref parsing.

@agrrr3 In #3211 I used `std::promise` to use as thread safe barrier to wait in main thread for named value parser finished. > Can I also somehow wait IApp::StartBackgroundParsing on...

> Waiting only for the NamedValueRefParser won't suffice though - you/we need to wait for all the parsers which may parse valuerefs to finish. I only re-implemented current `WaitForPending` in...