[PATCH v2] util: Fix two corner-cases in boolean term quoting function

[David Bremner]

Austin Clements <amdragon at MIT.EDU> writes:

> Previously, make_boolean_term did not quote empty boolean terms or
> boolean terms that started with '('.  These cases are incompatible
> with Xapian: empty terms cannot be omitted, and boolean terms that
> start with '(' trigger an alternate term quoting syntax.

pushed,

d