Fixed export of tables with VIRTUAL columns

Apparently the flag differs between MySQL and MariaDB versions, so let's
check both.

Fixes #13647

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

ChangeLog

@@ -10,6 +10,7 @@ phpMyAdmin - ChangeLog
 - issue #13604 Fixed crash on invalid ordering data
 - issue #13639 Fixed error when browsing non SELECT results
 - issue #13533 Fixed saving column to display
+- issue #13647 Fixed export of tables with VIRTUAL columns
 
 4.7.4 (2017-08-23)
 - issue #13415 Remove shadow from the logo

libraries/Table.php

@@ -1558,7 +1558,7 @@ class Table
                     $value = Util::backquote($value);
                 }
 
-                if (strpos($column['Extra'], 'GENERATED') === false) {
+                if (strpos($column['Extra'], 'GENERATED') === false && strpos($column['Extra'], 'VIRTUAL') === false) {
                     array_push($ret, $value);
                 }
             }