Fix /users/0

The website API now reports userid '0' as an unregistered user.

Apparently PHP treats the string '0' as falsy. In the interests of
not overhauling literally all our APIs, I've decided to only change
the code in the website API. The rest doesn't need to be changed
because number-only userids haven't been allowed for a very long
time.

Fixes smogon/pokemon-showdown#7704

lib/ntbb-session.lib.php

@@ -404,6 +404,7 @@ function validatePasswordResetToken($token) {
 	function getUser($userid=false) {
 		global $psdb, $curuser;
 
+		if ($userid === '0') return false;
 		if (is_array($userid)) $userid = $userid['userid'];
 		$userid = $this->userid($userid);
 		if (!$userid ||

website/users.php

@@ -84,10 +84,14 @@
 	'gen1ou' => '[Gen 1] OU',
 );
 
-if (@$_REQUEST['user']) {
-	$userid = $users->userid(@$_REQUEST['user']);
-
-	if (!$userid) {
+if (isset($_REQUEST['user']) && strlen($_REQUEST['user'])) {
+	$userid = $users->userid($_REQUEST['user']);
+	// 0 is falsy
+	// I'm hardcoding here to fix a crash, but the rest of the system
+	// should continue to reject 0 as a valid userid
+	if ($_REQUEST['user'] === '0') $userid = '0';
+
+	if (!strlen($userid)) {
 		header('HTTP/1.1 404 Not Found');
 		die("Invalid userid");
 	}
@@ -113,7 +117,7 @@
 }
 
 if ($authLevel >= 3) {
-	file_put_contents(__DIR__ . '/../config/altaccesslog.txt', "{$curuser['username']} - $userid\n", FILE_APPEND);
+	//file_put_contents(__DIR__ . '/../config/altaccesslog.txt', "{$curuser['username']} - $userid\n", FILE_APPEND);
 }
 
 if (isset($_REQUEST['json'])) {