Simplify IP address validation

- check IPv4 and IPv6 in one call
- type strict checking of return value

See issue #12389

Signed-off-by: Michal Čihař <michal@cihar.com>

libraries/ip_allow_deny.lib.php

@@ -33,11 +33,10 @@ function PMA_getIp()
     $trusted_header_value
         = PMA_getenv($GLOBALS['cfg']['TrustedProxies'][$direct_ip]);
     $matches = array();
-    // the $ checks that the header contains only one IP address,
-    // ?: makes sure the () don't capture
-    $is_ip = (filter_var($trusted_header_value, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6) || filter_var($trusted_header_value, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4));
+    // checks that the header contains only one IP address,
+    $is_ip = filter_var($trusted_header_value, FILTER_VALIDATE_IP);
 
-    if ($is_ip) {
+    if ($is_ip !== false) {
         // True IP behind a proxy
         return $trusted_header_value;
     }