fix: setLabelRef

[ghost]

There is no setter of labelRef. So labelRef is always undefined, and cannot executive this code:

protected updateSelection() {
      ...

      const selectedIndex = this.MDComponent.selectedIndex;
      if (selectedIndex === 0) {
        if (this.labelRef) {
          this.labelRef.classList.remove('mdc-floating-label--float-above');
        }
      } else {
        if (this.labelRef) {
          this.labelRef.classList.add('mdc-floating-label--float-above');
        }
      }
    }
  }

So I fix it!

before:

after: