While we do not support MyISAM anymore, the migration still try some basic detection and provide appropriate processing. The detection was done by finding "ENGINE=MyISAM" inside the answer to "SHOW CREATE TABLE xwikidoc;". But this seems to not be working on some DBs.
This patch use an alternative method, which is checking the second column of "SHOW TABLE STATUS LIKE 'xwikidoc';" to be equals to "MyISAM". I hope this will prove to be more reliable. At least, it fix the DB on which the issue was encountered.