Fixed mortar driver randomly leaving gunner behind

[robert-franklin]

I relocate my mortar teams after every fire mission so that they don't get attacked by QRF or counter-batteried. Sometimes the driver would drive off, leaving the gunner behind and forcing him to walk to the next position or to die to a QRF.

This change fixes that by forcing the driver to a speed of 0 until the gunner is in a vehicle, then resetting the speed.

[Barbolani77]

Hi!

This is not 100% correct, but anyway I am working on some reliability improvements on this script as it drops errors when you dismiss a mortar group, so I will include your forcespeed idea.