Dan't accessing attr of None (`manifest` subcmd)

If d.remote is None, this code failed for obvious reasons.  This is a
simple fix.

Change-Id: I413756121e444111f1e3c7dc8bc8032467946c13

manifest_xml.py

@@ -233,7 +233,9 @@ class XmlManifest(object):
       e.setAttribute('name', name)
       if relpath != name:
         e.setAttribute('path', relpath)
-      remoteName = d.remote.remoteAlias or d.remote.name
+      remoteName = None
+      if d.remote:
+          remoteName = d.remote.remoteAlias or d.remote.name
       if not d.remote or p.remote.name != remoteName:
         e.setAttribute('remote', p.remote.name)
       if peg_rev: