convert/svn: fix backtrace in tags discovery (issue1742)

hgext/convert/subversion.py

@@ -455,8 +455,9 b' class svn_source(converter_source):'
                 # Here/tags/tag.1 discarded as well as its children.
                 # It happens with tools like cvs2svn. Such tags cannot
                 # be represented in mercurial.
-                addeds = dict((p, e.copyfrom_path) for p, e
-                              in origpaths.iteritems() if e.action == 'A')
+                addeds = dict((p, e.copyfrom_path) for p, e 
+                              in origpaths.iteritems() 
+                              if e.action == 'A' and e.copyfrom_path)
                 badroots = set()
                 for destroot in addeds:
                     for source, sourcerev, dest in pendings: