Improves the existing logic to hide tooltips in GlSparkline by
hiding the tooltip altogether when the data is invalid, as well
as hiding when the label/content is an empty string.

fix(GlSparklineChart): Prevent rendering blank or invalid tooltips

See merge request gitlab-org/gitlab-ui!4319



Merged-by: Peter Hegman <phegman@gitlab.com>
Approved-by: Kushal Pandya <kushal@gitlab.com>
Approved-by: Amelia Bauerly <abauerly@gitlab.com>
Approved-by: Peter Hegman <phegman@gitlab.com>
Reviewed-by: Peter Hegman <phegman@gitlab.com>
Reviewed-by: Alex Pennells <apennells@gitlab.com>
Co-authored-by: Alex Pennells <apennells@gitlab.com>

## [85.4.1](gitlab-org/gitlab-ui@v85.4.0...v85.4.1) (2024-06-26)

### Bug Fixes

* **GlSparklineChart:** Prevent rendering blank or invalid tooltips ([e4623521](gitlab-org/gitlab-ui@e4623521))