Don't consider no results an OAI harvest failure.

Author: aaxelb

share/harvest/oai.py

@@ -89,7 +89,7 @@ def fetch_page(self, url: furl, token: str=None) -> (list, str):
         parsed = etree.fromstring(resp.content, parser=etree.XMLParser(recover=True))
 
         error = parsed.xpath('//ns0:error', namespaces=self.namespaces)
-        if error:
+        if error and (len(error) > 1 or error[0].get('code') != 'noRecordsMatch'):
             raise OAIHarvestException(error[0].get('code'), error[0].text)
 
         records = parsed.xpath('//ns0:record', namespaces=self.namespaces)