BUG #12694: crash if the number of result rows is lower than gin_fuzzy_search_limit

The following bug has been logged on the website:

Bug reference:      12694
Logged by:          Olaf Gawenda
Email address:      olaf.gw@googlemail.com
PostgreSQL version: 9.4.0
Operating system:   Linux 3.2.0-4-amd64 #1 SMP Debian 3.2.65-1+deb7
Description:

the following sequence of commands get a crash if the numer of result rows
is lower than gin_fuzzy_search_limit:

create table test (t text, ts_vec tsvector);

insert into test (t) values (),(),(), ...; -- test data not posted

update test set ts_vec = to_tsvector('english', t);

create index on test using gin(ts_vec);
analyze test;
set enable_seqscan = off;
set gin_fuzzy_search_limit = 1000;

select t from test where ts_vec @@ to_tsquery('english', '...');