FIX: Null character replaced by blank

-The presence of the character '\0' was causing an error with some PDFs.
-It has been fixed by replacing all occurences of '\0' with ''.

pdfminer/cmapdb.py

@@ -230,6 +230,7 @@ class CMapDB(object):
 
     @classmethod
     def _load_data(klass, name):
+        name = name.replace("\0", "")
         filename = '%s.pickle.gz' % name
         log.info('loading: %r', name)
         cmap_paths = (os.environ.get('CMAP_PATH', '/usr/share/pdfminer/'),