Change Music linedef affects mid-level joiners even when the effect is supposed to be local only

We observed this bug both in Final Demo Zone and in CEZ1.

When Change Music has the ML_NOCLIMB flag checked, then all players are correctly affected.

But when ML_NOCLIMB flag is NOT checked, then only the local player is supposed to be affected.

For clients who were in the netgame BEFORE the level is loaded, this works correctly and the music change is not triggered for them.

But for clients who join the netgame MID-LEVEL, then Change Music will trigger for these clients incorrectly. This persists until a new level is loaded.