nodetree: simplify a conditionnal in shortesthexnodeidprefix

instead of try to catch some attribute error, we could just nicely look if the
attribute will be available. This make the code simpler to follow and less error
prone since we no longer rely on a wider attribute catching.

Differential Revision: https://phab.mercurial-scm.org/D7651

mercurial/scmutil.py

@@ -545,12 +545,10 b' def shortesthexnodeidprefix(repo, node, '
             if cache is not None:
                 nodetree = cache.get(b'disambiguationnodetree')
             if not nodetree:
-                try:
+                if util.safehasattr(parsers, 'nodetree'):
+                    # The CExt is the only implementation to provide a nodetree
+                    # class so far.
                     nodetree = parsers.nodetree(cl.index, len(revs))
-                except AttributeError:
-                    # no native nodetree
-                    pass
-                else:
                     for r in revs:
                         nodetree.insert(r)
                     if cache is not None: