pg_upgrade: Fix inconsistency in memory freeing

The function in charge of freeing the memory from a result created by
PQescapeIdentifier() has to be PQfreemem(), to ensure that both
allocation and free come from libpq.

One spot in pg_upgrade was not respecting that for pg_database's
datlocale (daticulocale in v16) when the collation provider is libc (aka
datlocale/daticulocale is NULL) with an allocation done using
pg_strdup() and a free with PQfreemem().  The code is changed to always
use PQescapeLiteral() when processing the input.

Oversight in 9637badd9f.  This commit is similar to 48e4ae9a07 and
5b94e27534.

Author: Michael Paquier <michael@paquier.xyz>
Co-authored-by: Ranier Vilela <ranier.vf@gmail.com>
Discussion: https://postgr.es/m/Z601RQxTmIUohdkV@paquier.xyz
Backpatch-through: 16

src/bin/pg_upgrade/pg_upgrade.c

@@ -383,6 +383,7 @@ set_locale_and_encoding(void)
 	char	   *datcollate_literal;
 	char	   *datctype_literal;
 	char	   *daticulocale_literal = NULL;
+	char	   *daticulocale_src;
 	DbLocaleInfo *locale = old_cluster.template0;
 
 	prep_status("Setting locale and encoding for new cluster");
@@ -396,12 +397,10 @@ set_locale_and_encoding(void)
 	datctype_literal = PQescapeLiteral(conn_new_template1,
 									   locale->db_ctype,
 									   strlen(locale->db_ctype));
-	if (locale->db_iculocale)
+	daticulocale_src = locale->db_iculocale ? locale->db_iculocale : "NULL";
 	daticulocale_literal = PQescapeLiteral(conn_new_template1,
-											   locale->db_iculocale,
-											   strlen(locale->db_iculocale));
-	else
-		daticulocale_literal = pg_strdup("NULL");
+										   daticulocale_src,
+										   strlen(daticulocale_src));
 
 	/* update template0 in new cluster */
 	if (GET_MAJOR_VERSION(new_cluster.major_version) >= 1500)