elementary: Check for valid focus manager before starting do loop

Apparently there are cases where efl_ui_focus_object_focus_manager_get
can return NULL. In order to trap for this, we can simply modify the
do loop slightly and check for a valid manager before we actually
start looping

Test Case: elementary_test -to "Panel Scrollable" and click Toggle
button

ref T7030

Differential Revision: https://phab.enlightenment.org/D6704