engine: client: prevent memory corruption on old protocol when server didn't sent local player info in delta at spawn

engine/client/cl_pmove.c

@@ -824,6 +824,27 @@ static void CL_SetupPMove( playermove_t *pmove, const local_state_t *from, const
 	cd = &from->client;
 
 	pmove->player_index = ps->number - 1;
+
+	// a1ba: workaround bug on old protocol where the server refuse to send
+	// our local player in delta. cl.playernum, in theory, must be equal
+	// to our local player index anyway
+	// this might not be a real solution, since everything else will be bogus
+	// but we need to properly run prediction and avoid potential memory
+	// corruption
+	// either debug this, or remove when old protocol will be dropped!!!
+	if( cls.legacymode )
+	{
+		if( pmove->player_index < 0 )
+		{
+			pmove->player_index = bound( 0, cl.playernum, cl.maxclients - 1 );
+		}
+		else
+		{
+			// if this happens, record a demo and send it to a1ba
+			Host_Error( "%s: ps->number == %d\n", __func__, ps->number );
+		}
+	}
+
 	pmove->multiplayer = (cl.maxclients > 1);
 	pmove->runfuncs = runfuncs;
 	pmove->time = time * 1000.0f;