hooks: fix hooks not firing if prechangegroup was set (issue4934) We need to call delayupdate again after writing to the changelog. Otherwise the prechangegroup hook consumes the delayupdate subscription and future hooks don't see the pending changes (see issue 4934 for more details). Adds a test that triggers the prechangegroup hook before the pretxnchangegroup hook and verifies that the output of pretxnchangegroup doesn't change.