fix: createfolders setting is ignored if readonly is True

If 'readonly' is True, folders shouldn't be created (regardless of
'createfolders' option). With old behavior, instead folders were always created
when 'readonly' is True (even if 'createfolders' was also False), which is a
serious bug (offlineimap was creating folders in all read-only repositories).
'createfolders' should only play a role if 'readonly' is False, in which case
folders should only be created if 'createfolders' is True.

Submitted-by: Vladimir Nesov <robotact@gmail.com>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/repository/Base.py

@@ -134,7 +134,7 @@ class BaseRepository(CustomConfig.ConfigHelperMixin, object):
 
         It is disabled by either setting the whole repository
         'readonly' or by using the 'createfolders' setting."""  
-        return self._readonly or self.getconfboolean('createfolders', True)
+        return (not self._readonly) and self.getconfboolean('createfolders', Tr
 
     def makefolder(self, foldername):
         """Create a new folder"""