Only check errno if getpwuid() fails

Checking errno otherwise is unspecified.

slock.c

@@ -67,10 +67,12 @@ getpw(void) { /* only run as root */
 
 	errno = 0;
 	pw = getpwuid(getuid());
+	if (!pw) {
 		if (errno)
 			die("slock: getpwuid: %s\n", strerror(errno));
-	else if (!pw)
+		else
 			die("slock: cannot retrieve password entry (make sure to suid or sgid slock)\n");
+	}
 	endpwent();
 	rval =  pw->pw_passwd;