Don't call update_current to set the input focus
Don't try to focus the focused node
Add missing return statement
Revert "Don't try to focus the focused node"

This reverts commit 92292f834fecec6aaa7ebdb714f0c573c0090e1b.

The `n == mon->desk->focus` appears after remove_node, so we can't
return in this case in `focus_node` after all.
Ignore _NET_ACTIVE_WINDOW for the focused node
Check to make sure the fence ratio is specified

Fixes a missing check for NULL.