lib: Document that notmuch_query_count_messages may return 0 if an exception occurs

This isn't a behavioral change---just a calrification in the documentation.

1 files changed, 3 insertions, 0 deletions

diff --git a/lib/notmuch.h b/lib/notmuch.h
index 921b0fcf..54616336 100644
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -506,6 +506,9 @@ notmuch_threads_destroy (notmuch_threads_t *threads);
  *
  * This function performs a search and returns Xapian's best
  * guess as to number of matching messages.
+ *
+ * If a Xapian exception occurs, this function may return 0 (after
+ * printing a message).
  */
 unsigned
 notmuch_query_count_messages (notmuch_query_t *query);