Fix config reader bug that overrode false values if default was set to true

Fixes #20

Since we have a value that is literally `false`, the `||=` on line 43 was all "Okay, you don't exist, going on to the default value, then!" which meant that Double Union applications would be perpetually open with this bug, which would be just untenable.

:pineapple: :boom: :pineapple: