Handle empty statement in psycopg instrumentation

[Holi0317]

Fixes #2643

Description

Handle case where statement can be empty in psycopg

Fixes #2643

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Added unit test cases for empty string query

Does This PR Require a Core Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

See contributing.md for styleguide, changelog guidelines, and more.

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Holi0317 / name: Hollis Wu (d1ec928, a9babb3, 85b5014, ec7cff1, 2f00441)
• ✅ login: lzchen / name: Leighton Chen (76233d4)

[xrmx]

Nice catch!