IMAP: UIDPLUS: correctly warn about weird responses from some servers

Github-ref: https://github.com/OfflineIMAP/offlineimap/issues/455
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/IMAP.py

@@ -686,6 +686,8 @@ class IMAPFolder(BaseFolder):
                     return 0
                 try:
                     uid = int(resp[-1].split(' ')[1])
+                except ValueError as e:
+                    uid = 0 # Definetly not what we should have.
                 except Exception as e:
                     raise OfflineImapError("Unexpected response: %s"% str(resp),
                         OfflineImapError.ERROR.MESSAGE)