fix: QSelect does not show placeholder text when using chips (fix #2003)

[michaelbaur]

Since it works without chips, I propose to use the same code path for chips if there no selected items

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
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Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

The PR fulfills these requirements:

• It's submitted to the dev branch and not the master 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 with all Quasar themes
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on a Electron app
• Any necessary documentation has been added or updated in the docs (for faster update click on "Suggest an edit on GitHub" at bottom of page) 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 open a suggestion issue first and wait for approval before working on it)

Other information:

[rstoenescu]

Hi,

Thanks for contributing! Pushed this fix (with a little change) to latest v0.17. Is there a possibility for you to upgrade to latest? Otherwise it would be a real hassle (lots of time lost) to release a new old v0.15 :(

[michaelbaur]

Thanks for the swift reaction. Yes, we can update to v0.17, no worries. I just wasn't sure about your bugfix policy and thus started from an old state.