Fix incorrectly reset selectedItem when custom value allowed

[web-padawan]

Fixes #622

Fixes vaadin/vaadin-time-picker#73

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This change is 

[platosha]

Reviewed 2 of 2 files at r1.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @web-padawan)

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src/vaadin-combo-box-mixin.html, line 777 at r1 (raw file):

      const valueIndex = this._indexOfValue(value, this.filteredItems);
      const item = valueIndex > -1 && this.filteredItems[valueIndex];
      this.selectedItem = item ? item : null;

false should be a valid item to select, I think. Would be cleaner to check for item !== undefined instead.

[web-padawan]

Reviewable status: 1 of 2 files reviewed, 1 unresolved discussion (waiting on @platosha)

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src/vaadin-combo-box-mixin.html, line 777 at r1 (raw file):

Previously, platosha (Anton Platonov) wrote…

false should be a valid item to select, I think. Would be cleaner to check for item !== undefined instead.

Done.

[platosha]

Reviewed 1 of 1 files at r2.
Reviewable status: complete! all files reviewed, all discussions resolved

[tomivirkki]

Reviewed 1 of 2 files at r1, 1 of 1 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved