[1846] only show buyable trains in EMR

[benjaminxscott]

Fixes #10185

Before clicking "Create"

• Branch is derived from the latest master
• [NA] Add the pins 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

In EMR when a corp has enough money for a "weaker" variant but not enough for a pricer variant, the president is allowed to sell shares to afford the pricier one.

In this case, we should only show trains that can be purchased at those times

• Screenshots
  

• Any Assumptions / Hacks