BUG #8395: empty aclitem arrays are considered 1-dimensional

The following bug has been logged on the website:

Bug reference:      8395
Logged by:          Alexey Bashtanov
Email address:      bashtanov@imap.cc
PostgreSQL version: 9.1.9
Operating system:   Ubuntu linux 12.04
Description:

Empty aclitem arrays are considered 1-dimensional, but in general empty
arrays are 0-dimensional. It leads to the following problems:


STEPS TO REPRODUCE
1) install fresh postgres, connect to it
2) select relacl, relacl = '{}'::aclitem[], (select aclexplode(relacl)),
array_length(relacl, 1) from pg_class where oid::regclass =
'pg_largeobject'::regclass;
3) select aclexplode('{}'::aclitem[]);


EXPECTED
2) {}, false, null, null
3) no error, zero-lines table


GOT
2)  relacl | ?column? | ?column? | array_length
--------+----------+----------+--------------
 {}     | f        |          |            0
3) ERROR:  ACL arrays must be one-dimensional


also it can be reproduced on some 9.2 version