perf: fix perfrevlogrevisions --reverse

Currently, 'endrev' equals `len(revlog)`, a revision that does not exist.

When asking for the reverse order, the arguments passed to xrange are
`xrange(len(revlog), startrev)` which then crash.

We need to offset 'endrev' by one so we don't crash anymore. Also, we offset
'startrev' to ensure we get the same number of revisions with and without the
`--reverse` option.

Differential Revision: https://phab.mercurial-scm.org/D5228

contrib/perf.py

@@ -1553,7 +1553,7 b' def perfrevlogrevisions(ui, repo, file_='
         dist = opts[b'dist']
 
         if reverse:
-            beginrev, endrev = endrev, beginrev
+            beginrev, endrev = endrev - 1, beginrev - 1
             dist = -1 * dist
 
         for x in _xrange(beginrev, endrev, dist):