Fix utf7 decode error not caught

Signed-off-by: Stéphane Albert <sheeprine@oh.its.fake.nullplace.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/imaputil.py

@@ -368,5 +368,5 @@ def decode_mailbox_name(name):
 
     try:
         return ret.decode('utf-7').encode('utf-8')
-    except UnicodeEncodeError:
+    except (UnicodeDecodeError, UnicodeEncodeError):
         return name