Fix last remaining uninitialized memory warnings

gcc (version 13) fails to properly analyze the code due to the loop
stop condition including `l != NULL`. Let's just help it out.

Author: Tristan Partin <tristan@neon.tech>
Discussion: https://www.postgresql.org/message-id/flat/CT6HJ3U8068R.3A8SJMV02D9BC@gonk

src/bin/pgbench/pgbench.c

@@ -2239,7 +2239,7 @@ evalStandardFunc(CState *st,
 {
 	/* evaluate all function arguments */
 	int			nargs = 0;
-	PgBenchValue vargs[MAX_FARGS];
+	PgBenchValue vargs[MAX_FARGS] = { 0 };
 	PgBenchExprLink *l = args;
 	bool		has_null = false;
 

src/bin/pgbench/pgbench.h

@@ -33,7 +33,7 @@ union YYSTYPE;
  */
 typedef enum
 {
-	PGBT_NO_VALUE,
+	PGBT_NO_VALUE = 0,
 	PGBT_NULL,
 	PGBT_INT,
 	PGBT_DOUBLE,