Avoid an AphrontParameterQueryException when running a typeahead project name query with mustHaveColumns when the search string is not the prefix of the project name.
Since rP9a1d59ad5bd51ef4bf56533db260cc9e11a54fe6, Phorge runs queries in two phases: First prefix, then content, to sort project results accordingly.
`PhabricatorTypeaheadDatasource::loadResultsForPhase()` first checks for `phase: prefix`. This query may return zero results.
Current code does not correctly handle this situation.
Thus make the code smoothly skip to the `content` query phase and not run a PhabricatorProjectColumnQuery with an empty project PHID array parameter.
Closes T16068