BUG #15578: Executing json_populate_recordset with an empty arraycauses a segmentation fault

The following bug has been logged on the website:

Bug reference:      15578
Logged by:          Greg Keegan
Email address:      gregk@stoddarts.com.au
PostgreSQL version: 11.1
Operating system:   CentOS Linux release 7.1.1503 (Core)
Description:

When executing json_populate_recordset/jsonb_populate_recordset with an
empty array, a segmentation fault occurs and the server process is
terminated. The issue occurs regardless of the type used. In previous
versions this would return null.

Example:
CREATE TYPE test_type AS (amount numeric, description text);
SELECT * FROM json_populate_recordset(null::test_type,'[]');

Log:
2019-01-07 13:46:58.196 AEST [1847] LOG:  server process (PID 4341) was
terminated by signal 11: Segmentation fault
2019-01-07 13:46:58.196 AEST [1847] DETAIL:  Failed process was running:
SELECT * FROM json_populate_recordset(null::test_type,'[]');
2019-01-07 13:46:58.196 AEST [1847] LOG:  terminating any other active
server processes
2019-01-07 13:46:58.202 AEST [4213] WARNING:  terminating connection because
of crash of another server process
2019-01-07 13:46:58.202 AEST [4213] DETAIL:  The postmaster has commanded
this server process to roll back the current transaction and exit, because
another server process exited abnormally and possibly corrupted shared
memory.
2019-01-07 13:46:58.202 AEST [4213] HINT:  In a moment you should be able to
reconnect to the database and repeat your command.
2019-01-07 13:46:58.210 AEST [1847] LOG:  all server processes terminated;
reinitializing
2019-01-07 13:46:58.884 AEST [4374] LOG:  database system was interrupted;
last known up at 2019-01-07 13:42:07 AEST
2019-01-07 13:46:59.565 AEST [4374] LOG:  database system was not properly
shut down; automatic recovery in progress
2019-01-07 13:46:59.592 AEST [4374] LOG:  redo starts at 29/CD051528
2019-01-07 13:46:59.593 AEST [4374] LOG:  invalid record length at
29/CD069AD0: wanted 24, got 0
2019-01-07 13:46:59.593 AEST [4374] LOG:  redo done at 29/CD069A98
2019-01-07 13:46:59.593 AEST [4374] LOG:  last completed transaction was at
log time 2019-01-07 13:46:44.868687+10
2019-01-07 13:46:59.708 AEST [1847] LOG:  database system is ready to accept
connections