doc: forbid further operations on a closed database

We could add many null pointer checks, but currently I don't see a use
case that justifies it.

diff --git a/lib/notmuch.h b/lib/notmuch.h
index cb46fc057d3e3ee91b7b9fcb5ae02667a2ab2c5f..a43e167c2f84a059d31ff0fa093fd2de2abb9908 100644 (file)
--- a/lib/notmuch.h
+++ b/lib/notmuch.h
@@ -331,7 +331,9 @@ notmuch_database_status_string (const notmuch_database_t *notmuch);
  * functions on objects derived from this database may either behave
  * as if the database had not been closed (e.g., if the required data
  * has been cached) or may fail with a
- * NOTMUCH_STATUS_XAPIAN_EXCEPTION.
+ * NOTMUCH_STATUS_XAPIAN_EXCEPTION. The only further operation
+ * permitted on the database itself is to call
+ * notmuch_database_destroy.
  *
  * notmuch_database_close can be called multiple times.  Later calls
  * have no effect.