[Information Leak] Identify enemy location with controlgroups

[elexis]

If you add a controlgroup to an enemy unit, then you can jump to the unit, even if it is inside the fog of war.

Steps to reproduce:

	-Start two instances of 0ad, host locally on the first instance & join with the second one
	-Start the game and for both players put diplomacy to neutral to prevent attacks
	-Move a unit of player 1 to the base of player 2
	-As player 2, create a controlgroup for the player 1 unit
	-As player 1, move the unit out of the base
	-As player 2, jump to the controlgroup

Expected result: Camera shouldn't move. Actual result: Camera moves to the correct position of the enemy, although it is inside the fog of war.

Additionnal Details : The follow unit function works as expected, since it stops when the enemy unit enters the fog of war. Also the GUI hides the information like health points, if the unit is inside the fog of war.

[Itms]

In 16367:

Check visibility of units before moving the camera to their position, when using selection groups.
Fixes #3065.

[elexis]

works!

[elexis]

Thanks to ffm for reporting it to me!