virdbus: Grab a ref as long as the while loop is executed

Grab a ref for info->bus (a DBus connection) as long as the while loop
is running. With the grabbed reference it is ensured that info->bus
isn't freed as long as the while loop is executed. This is necessary
as it's allowed to drop the last ref for the bus connection in a
handler.

There was already a bug of this kind in libdbus itself:
https://bugs.freedesktop.org/show_bug.cgi?id=15635.
Signed-off-by: NMarc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: NBoris Fiuczynski <fiuczy@linux.ibm.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

src/util/virdbus.c

@@ -198,8 +198,10 @@ static void virDBusWatchCallback(int fdatch ATTRIBUTE_UNUSED,
 
     (void)dbus_watch_handle(watch, dbus_flags);
 
+    dbus_connection_ref(info->bus);
     while (dbus_connection_dispatch(info->bus) == DBUS_DISPATCH_DATA_REMAINS)
         /* keep dispatching while data remains */;
+    dbus_connection_unref(info->bus);
 }