fix: overflow in the calculation expr

[kemingy]

This fixes the overflow test in

sqlparser-rs/tests/sqlparser_common.rs

Lines 14107 to 14117 in 0d2976d

	#[test]
	fn overflow() {
	let expr = std::iter::repeat_n("1", 1000)
	.collect::<Vec<_>>()
	.join(" + ");
	let sql = format!("SELECT {}", expr);
	let mut statements = Parser::parse_sql(&GenericDialect {}, sql.as_str()).unwrap();
	let statement = statements.pop().unwrap();
	assert_eq!(statement.to_string(), sql);
	}