[PATCH] lib: work around xapian bug with get_mset(0,0, x)

[David Bremner]

At least Fedora28 triggers this Xapian bug due to some toolchain change .

   https://bugzilla.redhat.com/show_bug.cgi?id=1546162

The underlying bug is fixed in xapian commit f92e2a936c1592, and
should be fixed in Xapian 1.4.6
---

I have verified this doesn't break the test suite in my environment,
but I would appreciate feedback from someone with a Fedora 28 test
platform.

 lib/query.cc | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/query.cc b/lib/query.cc
index d633fa3d..7fdf992d 100644
--- a/lib/query.cc
+++ b/lib/query.cc
@@ -652,9 +652,9 @@ _notmuch_query_count_documents (notmuch_query_t *query, const char *type, unsign
 	/*
 	 * Set the checkatleast parameter to the number of documents
 	 * in the database to make get_matches_estimated() exact.
-	 * Set the max parameter to 0 to avoid fetching documents we will discard.
+	 * Set the max parameter to 1 to avoid fetching documents we will discard.
 	 */
-	mset = enquire.get_mset (0, 0,
+	mset = enquire.get_mset (0, 1,
 				 notmuch->xapian_db->get_doccount ());
 
 	count = mset.get_matches_estimated();
-- 
2.16.3