[GEN][ZH] Fix inaudible UnableToSetRallyPoint audio event when misplacing a Rally Point

[Stubbjax]

The UnableToSetRallyPoint audio event cannot be heard because its player index is unassigned. This is now rectified and the logic matches the RallyPointSet audio event. This is a user-facing change - the player will now correctly hear the 'invalid action' sound when a rally point placement fails, similarly to when a building placement fails.

Audio events that do not specify an owning player are not expected to be valid.

if (owningPlayer == NULL) {
    DEBUG_CRASH(("Sound '%s' expects an owning player, but the audio event that created it didn't specify one.\n", ei->m_audioName.str()));
    return FALSE;
}

[xezon]

Nice. Could you perhaps attach a video? Would be interest to hear that.

[xezon]

Makes sense.

[xezon]

Title text improved.