修复SqlUtil.removeOuterOrderBy处理没有order by的语句导致异常问题（pr#4089@Github）

hutool-db/src/main/java/cn/hutool/v7/db/sql/SqlUtil.java

@@ -285,7 +285,8 @@ public class SqlUtil {
 	 */
 	public static String removeOuterOrderBy(final String selectSql) {
 		// 去除order by 子句
-		return ReUtil.getGroup1(PATTERN_ORDER_BY, selectSql);
+		final String sql = ReUtil.getGroup1(PATTERN_ORDER_BY, selectSql);
+		return sql == null ? selectSql : sql;
 	}
 
 	/**

hutool-db/src/test/java/cn/hutool/v7/db/sql/Issue4066Test.java

@@ -28,4 +28,15 @@ public class Issue4066Test {
 
 		assertEquals("SELECT id, name, age FROM users WHERE status = 'active'", result);
 	}
+
+	/**
+	 * 测试不含Order by的语句
+	 */
+	@Test
+	public void removeOuterOrderByTest3() {
+		final String sql = "SELECT * FROM users";
+		final String result = SqlUtil.removeOuterOrderBy(sql);
+
+		assertEquals("SELECT * FROM users", result);
+	}
 }