Problem with postgresql backend

Hello, 

I was getting:
undefined method `[]' for nil:NilClass
in this line: 
node['pure-ftpd'][backend]['disabled_queries'].each 

I noticed that  node['pure-ftpd']['backend'].eql? backend only applies to 
'template node['pure-ftpd']["#{backend}.conf"] do' block and not to all '["mysql", "postgresql"].each do' block and that causes error. I moved 'if' statement and now everything works fine for me.

If you agree with my changes, please accept PR.

Thanks!