Zero-cost engine config gets unlocked despite lacking tech

[lpgagnon]

Before:

after:

Initially the rd0110 config is correctly non-purchasable because 1965 Orbital Rocketry hasn't been researched; but after clicking to purchase rd0107, rd0110 is also unlocked.

Bug doesn't occur after giving rd0110 an extra, non-shared ECM; it remains locked and non-unlockable.

Reporting here because I'm guessing it has to do with #300