convert: fix svn crash when svn.ra.get_log calls back with orig_paths=None

get_log started calling back with orig_paths=None on Fedora 20 with
subversion-1.8.3. That broke test-convert-svn-source.t .

There used to be some handling of that situation until e8f4e40f285a apparently
broke it. This patch restores what seems to be the most obvious handling of the
situation.

hgext/convert/subversion.py

@@ -91,10 +91,11 b' def get_log_child(fp, url, paths, start,'
                   discover_changed_paths=True, strict_node_history=False):
     protocol = -1
     def receiver(orig_paths, revnum, author, date, message, pool):
+        paths = {}
         if orig_paths is not None:
             for k, v in orig_paths.iteritems():
-                orig_paths[k] = changedpath(v)
-        pickle.dump((orig_paths, revnum, author, date, message),
+                paths[k] = changedpath(v)
+        pickle.dump((paths, revnum, author, date, message),
                     fp, protocol)
 
     try: