BUG #12845: The GB18030 encoding doesn't support Unicode characters over 0xFFFF

The following bug has been logged on the website:

Bug reference:      12845
Logged by:          Arjen Nienhuis
Email address:      a.g.nienhuis@gmail.com
PostgreSQL version: 9.3.5
Operating system:   Ubuntu Linux
Description:

Step to reproduce:

In psql:

arjen=> select convert_to(chr(128512), 'GB18030');

Actual output:

ERROR:  character with byte sequence 0xf0 0x9f 0x98 0x80 in encoding "UTF8"
has no equivalent in encoding "GB18030"

Expected output:

 convert_to
------------
 \x9439fc36
(1 row)