R1:340a293870c5

Fix an async display issue for tokenizer/typeahead results

Summary:
Ref T4420. After the changes to the tokenizer, I sometimes do this:

- Type something like "diff" into a project typeahead.
- Select "differential".
- A fraction of a second later, the typeahead pops back open.

This is because I selected the result from a partial query (like "diff" running against the "di" results) and then the full results of the "diff" query came back to the browser.

Instead, when showing results, require that…