fix(VAutocomplete): don't count search as dirty if it is empty

[Djaler]

Description

fixes #12958

Motivation and Context

The issue is regression after #12415
Search should not be counted as dirty when empty string in VCombobox, but not in VAutocomplete

How Has This Been Tested?

Visually on the markup from #12958 (https://codepen.io/djaler/pen/ZEpmazq) and from #12322 (https://codepen.io/MatthewAry/pen/BaKgBNq)

Types of changes

• 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)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and backwards compatible changes and next for non-backwards compatible changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)