Bugfix: Warp pointer to the correct window when using the 'focus' command

Bugfix: Warp pointer to the correct window when using the 'focus' command

Comment in the code makes the fix clear, I think.

Steps to reproduce the issue:
1) On the right monitor, open two terminals (h-split workspace)
2) 'i3 mark foo' on the right terminal
3) Focus the left terminal
4) Switch to the left monitor
5) i3 '[con_mark="foo"] focus'
6) the left window will contain the pointer (and is focused for a short period
   of time, or even permanently due to race conditions)