crush: insert_item returns on error if bucket name is invalid

crush: insert_item returns on error if bucket name is invalid

A bucket name may be created as a side effect of insert_item. All names
in the loc argument are checked for validity at the beginning of the
method and an error is returned immediately if one is found. This allows
to not check for errors when setting the name of an item later on.

Signed-off-by: Loic Dachary <loic@dachary.org>