sim: make sure we unexport the SIM object when destroying it

Usually, if not always, the connection stored in the SIM object never exists
when disposing it, as we clear the connection property in the Modem object
before destroying it, and both properties are bound. But just in case, in order
to avoid ending up with a zombie object in DBus, we make sure we unexport it.

src/mm-sim.c

@@ -1185,8 +1185,12 @@ dispose (GObject *object)
 {
     MMSim *self = MM_SIM (object);
 
-    if (self->priv->connection)
+    if (self->priv->connection) {
+        /* If we arrived here with a valid connection, make sure we unexport
+         * the object */
+        mm_sim_unexport (self);
         g_clear_object (&self->priv->connection);
+    }
 
     if (self->priv->modem)
         g_clear_object (&self->priv->modem);