The bug about the -and and -or

Hello.

I have encountered a bug.

It is a thing for the $prefix eq '' has not been taken into account, that the wrong -and and -or.

I added the script reveal the bug.
https://github.com/bokutin/Search-Query-Dialect-DBIxClass/blob/master/eg/bug_prefix.pl

% perl eg/bug_prefix.pl

    --> Dialect::Native
    +(name:o email:o)
    --> Dialect::SQL
    (name='o' OR email='o')
    --> Dialect::DBIxClass
    {
      "-and" => [
        {
          "-and" => []
        }
      ]
    }


% perl -I lib eg/bug_prefix.pl

    --> Dialect::Native
    +(name:o email:o)
    --> Dialect::SQL
    (name='o' OR email='o')
    --> Dialect::DBIxClass
    {
      "-and" => [
        {
          "-or" => [
            \[
                "LOWER(name) LIKE ?",
                [
                  "plain_value",
                  "%o%"
                ]
              ],
            \[
                "LOWER(email) LIKE ?",
                [
                  "plain_value",
                  "%o%"
                ]
              ]
          ]
        }
      ]
    }

Please check.

Thank you to merge if it is good.

Cheers,
Tomohiro Hosaka