MFC r266444:
We have two functions from where a geom orphan method could be called:
g_orphan_register and g_resize_provider_event. Both are called from the
event queue. Also we have GEOM_DEV class, which does deferred destroy
for its consumers via g_dev_destroy (also called from the event queue).
So it is possible, that for some consumers an orphan method will be
called twice. This triggers panic in g_dev_orphan.
Check that consumer isn't already orphaned before call orphan method.
git-svn-id: svn://svn.freebsd.org/base/stable/10@266970
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