[1871] Should not be able to crossbuy after issuing shares

[philcampeau]

Fixes #10069

Before clicking "Create"

• Branch is derived from the latest master
• Add the pins or archive_alpha_games label if this change will break existing games
• Code passes linter with docker compose exec rack rubocop -a
• Tests pass cleanly with docker compose exec rack rake

Implementation Notes

Explanation of Change

According to the rules of the game, a company cannot cross-buy after issuing shares. This prevents that from happening.

Screenshots

Any Assumptions / Hacks

Any games where a cross-buy has occurred after issuing shares would need to be pinned or archived.