SNMP polling broken for MYSQL application

In the past there was a hack at the top of ./incldues/polling/aaplications/mysql.inc.php which would check if the mysql data would exist in the agent data array (currently still exists in the nginx file) and if not it will attempt to retrieve the data via snmp. This was removed in recent commits. This in turn broke all snmp compatibility with mysql. Until a cleaner method is implemented to manage snmp and unix-agent polling for existing applications, a simple fix can be implemented to fix this issue. Diff has been attached.

Best Regards,

Almir Kadric