Don't send a netxcmd when using addfile outside of netgame

Was supposed to be happening already, but `multiplayer` is a useless variable...

src/d_netcmd.c

@@ -4484,7 +4484,7 @@ static void Command_Addfile(void)
 		}
 
 		// Add file on your client directly if it is trivial, or you aren't in a netgame.
-		if (!(netgame || multiplayer) || musiconly)
+		if (!netgame || musiconly)
 		{
 			P_AddWadFile(fn);
 			addedfiles[numfilesadded++] = fn;