tools: xend: tolerate empty state/*.xml

Bugzilla 1680: Xend fails to start if /var/lib/xend/state/*.xml are empty
which I get often when replacing the Xen hypervisor with a newer version.

This can be easily be reproduced under Fedora Core 16 by installing
xen RPMs and then replacing the xen.gz with a newer version.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Anthony Low <shinji@pikopiko.org>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/xend/XendStateStore.py

@@ -101,6 +101,9 @@ class XendStateStore:
         if not os.path.exists(xml_path):
             return {}
 
+        if not os.path.getsize(xml_path) == 0:
+            return {}
+
         dom = minidom.parse(xml_path)
         root = dom.documentElement
         state = {}