[Genhis] [2.0.15] The TechnologyPrototype flag essential is always false

[Villfuk02]

In control.lua force.technologies[tech].prototype.essential always returns false.
For example when I do /c print(game.player.force.technologies["logistic-science-pack"].prototype.essential), it prints false.

However, in the in-game prototype explorer, it shows true for the correct technologies.

[Genhis]

Thanks for the report. It was a copy-paste mistake; fixed for the next release.