This change fixes the failure of the LibraryTest.filterByPublisher
unit-test broken by the previous commit.
The previous approach used in `publisherQuery()` for building a phrase
query enforcing the specified prefix for all terms fails if
1. the input phrase contains a non-word term that Xapian's query parser
doesn't like (e.g. a standalone ampersand character, 1/2, a#1, etc);
2. the input phrase contains at least three terms that Xapian's query
parser has no issue with.
Using the `quest` tool (coming with xapian-tools under Ubuntu) the
issue can be demonstrated as follows:
```
$ quest -o phrase -d some_xapian_db "Energy & security"
Parsed Query: Query((energy@1 PHRASE 11 Zsecur@2))
Exactly 0 matches
MSet:
$ quest -o phrase -d some_xapian_db "Energy & security act"
UnimplementedError: OP_NEAR and OP_PHRASE only currently support leaf subqueries
$ quest -o phrase -d some_xapian_db 'Energy 1/2 security act'
UnimplementedError: OP_NEAR and OP_PHRASE only currently support leaf subqueries
$ quest -o phrase -d some_xapian_db "Energy a#1 security act"
UnimplementedError: OP_NEAR and OP_PHRASE only currently support leaf subqueries
```
The problem comes from parsing the query with the default operation set
to `OP_PHRASE` (exemplified by the `-o phrase` option in above
invocations of `quest`). A workaround is to parse the phrase with a
default operation of `OP_OR` and then combine all the terms with
`OP_PHRASE`.
Besides stemming should be disabled in order to target an exact phrase
match (save for the non-word terms, if any, that are ignored by the
query parser).
Moved the `filter.hasQuery()` check inside `buildXapianQuery()`.
`Library::filterViaBookDB()` only cares if the query that is going to be
run on the book DB would match all documents. The rest of changes
related to enhancing the usage of Xapian for the catalog search will
happen inside `buildXapianQuery()` and `updateBookDB()`.
Now the LibraryTest.filterCheck unit-test validates the actual entries
returned by `Library::filter` (previously only the count of the results
was checked).
The new unit-test fails with a reason not expected before it was
written. The `Library::filter()` operation returns a correct result
after the call to `removeBookById()` (this was a surprise!) but it has
a side-effect of re-adding an empty book with the id still surviving
in the search DB (the emptiness of this re-created book doesn't allow
it to pass the other filtering criteria, which explains why the result
of `Library::filter()` is correct). Had to add a special check
to the new unit-test against that hidden side-effect of
`Library::removeBookById()` + `Library::filter()` combination.
