colorselector: Check return value of elm_layout_theme_set as other widgets do.
colorselector: Check return value of elm_layout_theme_set as other widgets do.

This fixes coverity CID 1273969.

tasn/elementary,rvandegrift/elementary,rvandegrift/elementary,FlorentRevest/Elementary,rvandegrift/elementary,FlorentRevest/Elementary,rvandegrift/elementary,tasn/elementary,FlorentRevest/Elementary,tasn/elementary,tasn/elementary,FlorentRevest/Elementary,tasn/elementary