Fixed version check when not connected to a database

Fixes #13437

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

ChangeLog

@@ -4,6 +4,7 @@ phpMyAdmin - ChangeLog
 4.7.3 (not yet released)
 - issue #13447 Large multi-line query removes Export operation and blanks query box options
 - issue #13445 Fixed rendering of query results
+- issue #13437 Fixed version check when not connected to a database
 
 4.7.2 (2017-06-29)
 - issue #13314 Make theme selection keep current server

libraries/VersionInformation.php

@@ -217,12 +217,16 @@ class VersionInformation
     }
 
     /**
-     * Returns the MySQL version
+     * Returns the MySQL version if connected to a database
      *
      * @return string MySQL version
      */
     protected function getMySQLVersion()
     {
-        return PMA_MYSQL_STR_VERSION;
+        if (defined('PMA_MYSQL_STR_VERSION')) {
+            return PMA_MYSQL_STR_VERSION;
+        } else {
+            return null;
+        }
     }
 }