log: fix crash on empty revision with --copies switch
If a revset is empty, .max() raises ValueError.
I don't see any reason to recompute the revs, so I made it reuse the one
returned by logcmdutil.getrevs(). If no revs specified by command line,
the endrev will be smartset.spanset(repo) + 1, which is basically the same
as len(repo), the default of getrenamedfn(). If --follow specified,
revs.max() points to the working parent, which seems more correct.
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Ran 16 tests in 0.000s
OK