bus: move BUS_DONT_DESTROY calls after asserts
    
    It's not useful to bump the reference count before checking if the object is
    NULL. Thanks to d40f5cc498 we can do this ;).
    
    Related to https://bugzilla.redhat.com/show_bug.cgi?id=1576084,
    https://bugzilla.redhat.com/show_bug.cgi?id=1575340,
    https://bugzilla.redhat.com/show_bug.cgi?id=1575350. I'm not sure why those two
    people hit this code path, while most people don't. At least we won't abort.
    
    (cherry picked from commit 7ae8edcd03f74da123298330b76c3fc5425042ef)
    
    Resolves: #1610397
    
    patch_name: 0020-bus-move-BUS_DONT_DESTROY-calls-after-asserts.patch
    present_in_specfile: true
    location_in_specfile: 20
    squash_commits: true