Обсуждение: pgsql: Fix ts_stat's failure on empty tsvector.

Log Message:
-----------
Fix ts_stat's failure on empty tsvector.
Also insert a couple of Asserts that check for stack overflow.
Bogus coding appears to be new in 8.4 --- older releases had a much
simpler algorithm here.  Per bug #5111.

Modified Files:
--------------
    pgsql/src/backend/utils/adt:
        tsvector_op.c (r1.24 -> r1.25)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/adt/tsvector_op.c?r1=1.24&r2=1.25)