BUG #15150: Reading uninitialised value in NISortAffixes (tsearch/spell.c)

The following bug has been logged on the website:

Bug reference: 15150
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 10.3
Operating system: Debian-8
Description:

When trying to installcheck hunspell_nl_nl
(https://github.com/postgrespro/hunspell_dicts)
(see
https://github.com/postgrespro/hunspell_dicts/blob/master/hunspell_nl_nl/sql/hunspell_nl_nl.sql)
under valgrind, I get the following diagnostics:

==00:01:05:53.421 20772== Conditional jump or move depends on uninitialised
value(s)
==00:01:05:53.422 20772== at 0x4EA2C6: NISortAffixes (spell.c:1966)
==00:01:05:53.423 20772== by 0x4E5AA5: dispell_init (dict_ispell.c:90)
==00:01:05:53.425 20772== by 0x5E83F1: OidFunctionCall1Coll
(fmgr.c:1332)
==00:01:05:53.426 20772== by 0x36427C: verify_dictoptions.part.2
(tsearchcmds.c:399)
==00:01:05:53.426 20772== by 0x365ED2: verify_dictoptions
(tsearchcmds.c:477)
==00:01:05:53.427 20772== by 0x365ED2: DefineTSDictionary
(tsearchcmds.c:460)
==00:01:05:53.427 20772== by 0x4DE511: ProcessUtilitySlow.isra.5
(utility.c:1293)
==00:01:05:53.427 20772== by 0x4DCC70: standard_ProcessUtility
(utility.c:944)
==00:01:05:53.427 20772== by 0x7334815: pgss_ProcessUtility
(pg_stat_statements.c:1062)
==00:01:05:53.427 20772== by 0x7FB5DE4: pathman_process_utility_hook
(hooks.c:946)
==00:01:05:53.427 20772== by 0x320E99: execute_sql_string
(extension.c:763)
==00:01:05:53.427 20772== by 0x320E99: execute_extension_script.isra.7
(extension.c:924)
==00:01:05:53.427 20772== by 0x32187B: CreateExtensionInternal
(extension.c:1529)
==00:01:05:53.427 20772== by 0x321DD7: CreateExtension
(extension.c:1718)

It looks that the following condition in NISortAffixes(IspellDict *Conf)
uses uninitialised ptr->issuffix:

if (ptr == Conf->CompoundAffix ||
ptr->issuffix != (ptr - 1)->issuffix ||