multiselectfilter plugin ignores optgroup labels

[poeboy]

The filter plugin ignores optgroup labels. If a user types in the group label, I would expect all the items in that group to show up in the filtered results.

[denpanosekai]

This issue is affecting me as well.

[luizsgpetri]

Me too

[luizsgpetri]

I was able to fix this issue, I'll add the PR link here once created.

[luizsgpetri]

Fix: #605