elm_panel: add exception handling in _drawer_close()
this fixes a bug with scrollable panel not being blocked
when it is closed. scroll is blocked in _anim_stop_cb()
which is called after elm_interface_scrollable_region_bring_in().
but if panel content is already at the target position, _anim_stop_cb()
is not called. so there is a need to check content's position and
handle the exceptional case.