Multi-track allows targeting units with stealth

Looks like a regression of some kind

The issue reports that Multi-track can target units with stealth and calls it a possible regression, but names no files, tests, reproduction steps, or expected behavior. Start by reproducing the targeting behavior in the mod and compare it with the prior working behavior. Done means stealth units can no longer be targeted by Multi-track, with a regression test or documented verification if the project provides one.

Written by the indexing model from the issue text.