Fix handling of responses to queries from metadata grabbers when prov…

…ided with no output, rather than the expected of output with no results.

git-svn-id: http://svn.mythtv.org/svn/trunk@27203 7dbf422c-18fa-0310-86e9-fd20926502f2

mythtv/bindings/python/MythTV/system.py

@@ -212,7 +212,12 @@ def _process(self, xml):
 
 class Grabber( System ):
     def _processMetadata(self, xml):
-        for item in etree.fromstring(xml).getiterator('item'):
+        try:
+            xml = etree.fromstring(xml)
+        except:
+            raise StopIteration
+
+        for item in xml.getiterator('item'):
             yield self.cls(item)
 
     def command(self, *args):