fix(ui): remove double border-top in no data scenario (fix #18006)

[SamVanini]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Documentation
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev branch (or v[X] branch)
• When resolving a specific issue, it's referenced in the PR's title (e.g. fix: #xxx[,#xxx], where "xxx" is the issue number)
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on an Electron app
• Any necessary documentation has been added or updated in the docs or explained in the PR's description.

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature (to avoid wasting your time, it's best to start a new feature discussion first and wait for approval before working on it)

Other information:
This PR removes the undesiderable double border in no data scenario

Fix #18006

[yusufkandemir]

I haven't tested your solution or my suggestion yet, but I'm leaving it here for now

Suggested change

	.q-table__bottom
	border-top: 1px solid $table-border-color
	&.q-table__bottom--nodata
	border-top: none
	.q-table__bottom
	&:not(&--nodata)
	border-top: 1px solid $table-border-color

[SamVanini]

I tried your proposal, and changed my own code accordingly. It works and it is much cleaner than my initial thought. Thanks for pointing me out this alternative !