Prevent removeFirst call on empty list.

The hoverItems list might get changed as a result of the sendHoverEvent
call, so it is safer to take the element out first.

Change-Id: I88c7380a2e4dd2297f9d0cfe01edc453ca525cb3
Reviewed-by: Jan Arne Petersen <jan.petersen@kdab.com>
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>