PAM-Auth child: log if result can't be reported

This fixes the followin GCC warning on modern Linux systems as well:

irc-login.c:     In function ‘Hello_User’:
irc-login.c:876: warning: ignoring return value of ‘write’,
                 declared with attribute warn_unused_result

src/ngircd/irc-login.c

@@ -873,7 +873,9 @@ Hello_User(CLIENT * Client)
 		/* Sub process */
 		Log_Init_Subprocess("Auth");
 		result = PAM_Authenticate(Client);
-		write(pipefd[1], &result, sizeof(result));
+		if (write(pipefd[1], &result, sizeof(result)) != sizeof(result))
+			Log_Subprocess(LOG_ERR,
+				       "Failed to pipe result to parent!");
 		Log_Exit_Subprocess("Auth");
 		exit(0);
 	}