(proxy) auth, don't quit when squid sends an empty string

src/etc/inc/squid.auth-user.php

@@ -36,7 +36,9 @@ openlog("squid", LOG_ODELAY, LOG_AUTH);
 $authFactory = new \OPNsense\Auth\AuthenticationFactory();
 
 $f = fopen("php://stdin", "r");
-while ($line = fgets($f)) {
+while (!(feof($f))) {
+    $line = fgets($f);
+    if ($line) {
         $fields = explode(' ', trim($line));
         $username = rawurldecode($fields[0]);
         $password = rawurldecode($fields[1]);
@@ -79,6 +81,7 @@ while ($line = fgets($f)) {
             syslog(LOG_WARNING, "user '{$username}' could not authenticate.\n");
             fwrite(STDOUT, "ERR\n");
         }
+    }
 }
 
 closelog();