Select first option on enter when search is enabled

[nichtich]

I stumbled upon this in my project but could reproduce in the demo with "example #5 - Autocomplete with async options" as well:

1. Type in "perl"
2. An async list is loaded with a single entry "Perl"
3. Press Enter
4. Nothing happens, but the first list entry should be selected

Note this issue is not about case-insensitive search! The async backend function could also return "Practical Extraction and Report Language" when searching for "perl". My use case is a search for languages where searching for the language names or codes returns language names, e.g. search "de" will show first list entry "German".