repository.list: refresh lock more frequently

under all circumstances, we must avoid that the lock
gets stale due to not being refreshed in time.

there is some internal rate limiting in _lock_refresh,
so calling it often should be no problem.

src/borg/repository.py

@@ -336,11 +336,11 @@ def list(self, limit=None, marker=None):
  list <limit> infos starting from after id <marker>.
  each info is a tuple (id, storage_size).
  """
- self._lock_refresh()
  collect = True if marker is None else False
  result = []
  infos = self.store.list("data") # generator yielding ItemInfos
  while True:
+ self._lock_refresh()
  try:
  info = next(infos)
  except StoreObjectNotFound: