correctly handle logically empty simple searches (i.e. any)

[gkleen]

Our users expect that typing any in simple search returns a list of all tickets; this also conforms to the inline documentation for the simple search feature.

During parsing the query any is mapped to the empty string. Thus all following "truthiness" checks treat the query as falsy, returning extremely unhelpful error messages instead of results.

This PR substitutes a default catch-all query iff the query is empty due to parsing. A truely empty query is cought earlier.

[elacour]

Looks like this PR can resolve https://rt.bestpractical.com/Ticket/Display.html?id=36902

[sunnavy]

A similar fix has been merged to 5.0-trunk, I'm closing this pull request.

Thanks!

-sunnavy