There's nothing to fix, that is intentional. Garrisons can never be completely wired off, Relic changed this a long time ago. If the last or only door is wired off, the wire becomes void.
You can use a V-shape wire though, then units can still enter but they'll get trapped once they try to exit.
(I assumed they would escape fine as my opponent wasn't an idiot but he couldn't get away at all)
While I missed the memo on that change, testing it now with SP/CE/Pio wire on Lienne again, the squad can't escape that house at all, even pressing retreat. Tried escaping whilst attributing friendly/neutral/hostile wire but the same result occurs - The wire's fully functional. I've tried exiting the other three sides with TAB just in case there's a funny shaped door like a window, but there really is only one door. Whatever they did to fix it back then, doesn't seem to work any more. Or at least not with this house.
It's not a big issue anyway I suppose, the vast majority of houses have more than one exit.