use server side offset if provided

pandora_client/__init__.py

@@ -1048,6 +1048,10 @@ class API(ox.API):
                         time.sleep(5)
                 if data and data.get('result') == 1:
                     done += len(chunk)
+                    if data.get('offset') not in (None, done):
+                        print 'server offset out of sync, continue from', data['offset']
+                        done = data['offset']
+                        f.seek(done)
                     with open(self._resume_file, 'w') as r:
                         json.dump({
                             'uploadUrl': uploadUrl,