Only add URL query if it's not empty

[RaeesBhatti]

📬 Issue #, if available:

✍️ Description of changes:
In the current state, the runtime adds a ? to every request URL even if the query was not set. This change fixes that behavior for AWS API Gateway V2 requests.

🔏 By submitting this pull request

• I confirm that I've ran cargo +nightly fmt.
• I confirm that I've ran cargo clippy --fix.
• I confirm that I've made a best effort attempt to update all relevant documentation.
• I confirm that my contribution is made under the terms of the Apache 2.0 license.

[calavera]

thanks!