[tracker] libtracker-data: Keep interface ref during close()

[Carlos Garnacho <carlosg src gnome org>]

commit 20d80abf54d29e2e74d772dd2af49e8be01bd3ff
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Nov 27 19:47:41 2016 +0100

    libtracker-data: Keep interface ref during close()
    
    The cursor may tear down the last interface instance, which
    leads to invalid writes when poking its memory during unlock.

 src/libtracker-data/tracker-db-interface-sqlite.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/libtracker-data/tracker-db-interface-sqlite.c 
b/src/libtracker-data/tracker-db-interface-sqlite.c
index cb4f503..df30a21 100644
--- a/src/libtracker-data/tracker-db-interface-sqlite.c
+++ b/src/libtracker-data/tracker-db-interface-sqlite.c
@@ -2428,11 +2428,15 @@ tracker_db_cursor_close (TrackerDBCursor *cursor)
        }
 
        iface = cursor->ref_stmt->db_interface;
+
+       g_object_ref (iface);
        g_atomic_int_add (&iface->n_active_cursors, -1);
 
        tracker_db_interface_lock (iface);
        g_clear_pointer (&cursor->ref_stmt, tracker_db_statement_sqlite_release);
        tracker_db_interface_unlock (iface);
+
+       g_object_unref (iface);
 }
 
 static void