Fix check for empty dependencies on admin bar style loader tag filter

[Takshil-Kunadia]

Summary

Fixes #7766

• Added check for empty since deps is a non-nullable property of WP_Styles.

Checklist

• [ ] My code is tested and passes existing tests.
• [ ] My code follows the Engineering Guidelines (updates are often made to the guidelines, check it out periodically).

[Takshil-Kunadia]

Should we add the same checks here as well? https://github.com/ampproject/amp-wp/blob/79b1b7a5b00e2d4e5872b26c5f96469b244dca96/includes/class-amp-theme-support.php#L1404-L1414 https://github.com/ampproject/amp-wp/blob/79b1b7a5b00e2d4e5872b26c5f96469b244dca96/includes/class-amp-theme-support.php#L1426-L1435

[westonruter]

@Takshil-Kunadia sure, sounds good!