elementary: Avoid passing NULL in some win focus methods

Summary:
This one is rather harmless, as the NULL returned by this fuction is handled
correctly in all places, but this commit removes the runtime warning.

ref T7030

Test Plan: After this commit the warning disappears. Got the warning with win_example.

Reviewers: zmike, bu5hm4n, devilhorns

Reviewed By: devilhorns

Subscribers: netstar, cedric, committers

Tags: efl

Maniphest Tasks: T7030

Differential Revision: https://phab.enlightenment.org/D6538