Fix undefined index warning in installation.

diff --git a/install/index.php b/install/index.php
index f1547982c4534285ddbb7beeaf6dd2e00f3aaf7e..350c2f2d03e07bea2b52a419774a9fef6a972d81 100755 (executable)
--- a/install/index.php
+++ b/install/index.php
@@ -139,7 +139,7 @@
        }
 
        function is_server_https() {
-               return (!empty($_SERVER['HTTPS']) && ($_SERVER['HTTPS'] != 'off')) || $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https';
+               return (!empty($_SERVER['HTTPS']) && ($_SERVER['HTTPS'] != 'off')) || (!empty($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https');
        }
 
        function make_self_url_path() {