swaylock: Fix crash when unable to connect to wl
swaylock: Fix crash when unable to connect to wl

Prevent swaylock from crashing when it can't connect to wayland for
whatever reason. i.e. XDG_RUNTIME_DIR not set.

Fix #534

taiyu-len/sway,4e554c4c/sway,johalun/sway,sleep-walker/sway,mikkeloscar/sway,ptMuta/sway,mikkeloscar/sway,taiyu-len/sway,4e554c4c/sway,1ace/sway,ascent12/sway,1ace/sway,SirCmpwn/sway,ascent12/sway,ascent12/sway,sleep-walker/sway,1ace/sway,crondog/sway,taiyu-len/sway,crondog/sway