We actually “need” to wait a little for input to be released before
locking for cases where slock is spawned from other graphical
applications using keybindings.
This undoes the misbehaviour I introduced in c2f9757, sorry for the mess.
We want to know at once if slock failed or not to lock the screen, not
seing a black screen for a whole second (or two) and then die.
Thanks to ^7heo for reporting this.