querystring: fix stringify for empty array

Fixes #33910 (closed)

Currently querystring.stringify({a:1, b:[]}) return "a=1&" and querystring.stringify({a:1}) return "a=1" and querystring.stringify({a:[], b:[]}) return ""

If this PR is merged, first one will change to querystring.stringify({a:1, b:[]}) return "a=1".

I think that this is better for consistency.

Checklist

• tests and/or benchmarks are included
• commit message follows commit guidelines