changelog: abort on attempt to write wdir revision

Similar to the previous patch which prevented writing the null
revision to any revlog, but this is for the wdir revision.

Thanks to Jun for pointing this out.

Differential Revision: https://phab.mercurial-scm.org/D524

mercurial/changelog.py

@@ -14,6 +14,7 b' from .node import ('
     bin,
     hex,
     nullid,
+    wdirid,
 )
 
 from . import (
@@ -535,6 +536,9 b' class changelog(revlog.revlog):'
         # overlay over the standard revlog._addrevision to track the new
         # revision on the transaction.
         rev = len(self)
+        if node == wdirid: # nullid is checked in super method
+            raise error.RevlogError(_("%s: attempt to add wdir revision") %
+                                    (self.indexfile))
         node = super(changelog, self)._addrevision(node, rawtext, transaction,
                                                    *args, **kwargs)
         revs = transaction.changes.get('revs')