Mounted lasers can fire when attempting to deselect

[trigger-segfault]

Describe the issue
When using a tracker mounted laser, deselecting a vehicle can inconsistently fire before finishing the deselect. This is likely because the selection was made over the driver unit (and the unit has a lower object index in the listset?).

Expected behaviour
The tracker should never fire when trying to deselect to disable tracker mode.

Steps to reproduce

1. Equip a rock raider with any type of gun.
2. Turn on Action Stations so that it's easy to see a rock raider's position in a vehicle.
3. Spawn a Large Mobile Laser Cutter.
4. Tell the rock raider to get into the vehicle.
5. Select the LMSC and select again to enable the mounted laser.
6. Deselect just below where the Action Stations bubble is for the driver.

Additional information

• Time played this session: ~30-50 minutes.
• Level: Driller Night! (NoNerps enabled)
• Game speed: 20%-300%
• Graphics fix: dgVoodoo 2.55.4
• Using mods: None

---

Screenshots (optional)
On the left side the cursor is over a spot where deselecting will fire. On the right side the cursor is over a spot where deselecting won't fire.