MultiSelect group labels disappear when filtering

[john-oc]

Describe the bug

When groups are used with the MultiSelect and filtering is enabled, when any filter text is entered, all group labels are hidden.
Have created a pull request with a fix for this:- #3069

Reproducer

No response

PrimeVue version

3.17.0

Vue version

3.x

Language

ALL

Build / Runtime

Vue CLI App

Browser(s)

No response

Steps to reproduce the behavior

1. Add :filter="true" to the MultiSelect grouped example in the docs
2. Type a value in the filter which matches one or more options
3. Matching option(s) are shown, but all group labels disappear

Expected behavior

Group labels for options which match the filter should still be visible

[tugcekucukoglu]

Fixed #3069