bisect: simplify conditional in 'check_state'

Now that extra code about "updating" flag have been removed, we can simplify the
condition flow and remove a level.

mercurial/commands.py

@@ -836,12 +836,12 b' def bisect(ui, repo, rev=None, extra=Non'
     Returns 0 on success.
     """
     def checkstate(state):
-        if not state['good'] or not state['bad']:
+        if state['good'] and state['bad']:
+            return True
             if not state['good']:
                 raise error.Abort(_('cannot bisect (no known good revisions)'))
             else:
                 raise error.Abort(_('cannot bisect (no known bad revisions)'))
-        return True
 
     # backward compatibility
     if rev in "good bad reset init".split():