tools: xend: fix wrong condition check for xml file

In commit e8d40584, it intended to check xml file size and when empty will
return, the condition should be "if os.path.getsize(xml_path) == 0" rather
then "if not os.path.getsize(xml_path) == 0".

Signed-off-by: Chuang Cao <chuang.cao@oracle.com>
Signed-off-by: Joe Jin <joe.jin@oracle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>

xen-unstable changeset: 26088:dd64a1bdbe3a
Backport-requested-by: Ian Campbell <Ian.Campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

xen-4.2-testing changeset: 25905:82b61b99d15d
Backport-requested-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/python/xen/xend/XendStateStore.py

@@ -101,7 +101,7 @@ class XendStateStore:
         if not os.path.exists(xml_path):
             return {}
 
-        if not os.path.getsize(xml_path) == 0:
+        if os.path.getsize(xml_path) == 0:
             return {}
 
         dom = minidom.parse(xml_path)