Fix bogus affix-merging code.

NISortAffixes() compared successive compound affixes incorrectly,
thus possibly failing to merge identical affixes, or (less likely)
merging ones that shouldn't be merged.  The user-visible effects
of this are unclear, to me anyway.

Per bug #15150 from Alexander Lakhin.  It's been broken for a long time,
so back-patch to all supported branches.

Arthur Zakirov

Discussion: https://postgr.es/m/152353327780.31225.13445405496721177988@wrigleys.postgresql.org

src/backend/tsearch/spell.c

@@ -1963,8 +1963,10 @@ NISortAffixes(IspellDict *Conf)
 		if ((Affix->flagflags & FF_COMPOUNDFLAG) && Affix->replen > 0 &&
 			isAffixInUse(Conf, Affix->flag))
 		{
+			bool		issuffix = (Affix->type == FF_SUFFIX);
+
 			if (ptr == Conf->CompoundAffix ||
-				ptr->issuffix != (ptr - 1)->issuffix ||
+				issuffix != (ptr - 1)->issuffix ||
 				strbncmp((const unsigned char *) (ptr - 1)->affix,
 						 (const unsigned char *) Affix->repl,
 						 (ptr - 1)->len))
@@ -1972,7 +1974,7 @@ NISortAffixes(IspellDict *Conf)
 				/* leave only unique and minimals suffixes */
 				ptr->affix = Affix->repl;
 				ptr->len = Affix->replen;
-				ptr->issuffix = (Affix->type == FF_SUFFIX);
+				ptr->issuffix = issuffix;
 				ptr++;
 			}
 		}