Copy collencoding in CREATE COLLATION / FROM

This command used to compute the collencoding entry like when a
completely new collation is created.  But for example when copying the
"C" collation, this would then result in a collation that has a
collencoding entry for the current database encoding rather than -1,
thus not making an exact copy.  This has probably no practical impact,
but making this change keeps the catalog contents neat.
Reported-by: Tom Lane <tgl@sss.pgh.pa.us>

src/backend/commands/collationcmds.c

@@ -64,7 +64,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 	char	   *collcollate = NULL;
 	char	   *collctype = NULL;
 	char	   *collproviderstr = NULL;
-	int			collencoding;
+	int			collencoding = 0;
 	char		collprovider = 0;
 	char	   *collversion = NULL;
 	Oid			newoid;
@@ -126,6 +126,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 		collcollate = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collcollate));
 		collctype = pstrdup(NameStr(((Form_pg_collation) GETSTRUCT(tp))->collctype));
 		collprovider = ((Form_pg_collation) GETSTRUCT(tp))->collprovider;
+		collencoding = ((Form_pg_collation) GETSTRUCT(tp))->collencoding;
 
 		ReleaseSysCache(tp);
 
@@ -185,6 +186,8 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 				(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
 				 errmsg("parameter \"lc_ctype\" must be specified")));
 
+	if (!fromEl)
+	{
 		if (collprovider == COLLPROVIDER_ICU)
 			collencoding = -1;
 		else
@@ -192,6 +195,7 @@ DefineCollation(ParseState *pstate, List *names, List *parameters, bool if_not_e
 			collencoding = GetDatabaseEncoding();
 			check_encoding_locale_matches(collencoding, collcollate, collctype);
 		}
+	}
 
 	if (!collversion)
 		collversion = get_collation_actual_version(collprovider, collcollate);