Change Random() on negative values to always return zero.

Before, it would return huge, positive values (e.g. Random(-20) could produce 47384782) which leads to all kinds of trouble in script (like #968)
Make AdjustMoveToTarget more robust concerning large values.

Before, e.g. SetCommand("MoveTo", nil, 0,9999999) could freeze the engine for some time.
MineRescue: Fix adjusted flagpole radius to be used correctly in construction site connectivity preview.