[Bug]: Tests on _file_to_saveload.abstract_ftype in afterload do the wrong thing when joining as network client

[JGRennison]

Version of OpenTTD

master

Expected result

Scenario setup code guarded by _file_to_saveload.abstract_ftype == FT_SCENARIO should only run when actually loading a scenario.

Actual result

If a scenario is loaded, and then a network game is joined, _file_to_saveload.abstract_ftype is still set to FT_SCENARIO.

Company inauguration years are reset in the client but not the server. However, these are not used for anything important so should not cause a desync.

Steps to reproduce

See above