elm_colorselector: avoid passing null to efl functions

Summary:
this check already existed in the function but was not applied to the
entire function

ref T7030
Depends on D6322

Reviewers: bu5hm4n, Hermet, woohyun, devilhorns

Reviewed By: bu5hm4n

Subscribers: cedric, committers

Tags: efl

Maniphest Tasks: T7030

Differential Revision: https://phab.enlightenment.org/D6323