修复StrUtil.limitByByteLength在限制长度小于...时报错问题（issue#IDFTJS@Gitee）

hutool-core/src/main/java/cn/hutool/v7/core/text/CharSequenceUtil.java

@@ -3600,7 +3600,7 @@ public class CharSequenceUtil extends StrValidator {
 	 * @param charset        指定编码
 	 * @param maxBytesLength 最大字节数
 	 * @param factor         速算因子，取该编码下单个字符的最大可能字节数
-	 * @param appendDots     截断后是否追加省略号(...)
+	 * @param appendDots     截断后是否追加省略号...，如果maxBytesLength小于省略号长度，则不添加...
 	 * @return 限制后的长度
 	 */
 	public static String limitByteLength(final CharSequence str, final Charset charset, final int maxBytesLength,
@@ -3614,9 +3614,11 @@ public class CharSequenceUtil extends StrValidator {
 			return toStringOrNull(str);
 		}
 		//限制字节数
+		final int dotsBytesLength = "...".getBytes(charset).length;
 		final int limitBytes;
-		if (appendDots) {
-			limitBytes = maxBytesLength - "...".getBytes(charset).length;
+		// issue#IDFTJS 修正截断后追加省略号...导致超出限制长度的问题
+		if (appendDots && maxBytesLength > dotsBytesLength) {
+			limitBytes = maxBytesLength - dotsBytesLength;
 		} else {
 			limitBytes = maxBytesLength;
 		}
@@ -3628,7 +3630,7 @@ public class CharSequenceUtil extends StrValidator {
 		decoder.decode(bb, cb, true);
 		decoder.flush(cb);
 		final String result = new String(cb.array(), 0, cb.position());
-		if (appendDots) {
+		if (appendDots && maxBytesLength > dotsBytesLength) {
 			return result + "...";
 		}
 		return result;

hutool-core/src/test/java/cn/hutool/v7/core/text/CharSequenceUtilTest.java

@@ -544,4 +544,11 @@ public class CharSequenceUtilTest {
 	void concatTest() {
 		assertEquals("abc", CharSequenceUtil.concat(true, "a", "b", "c"));
 	}
+
+	@Test
+	public void issueTest() {
+		final String s = "abc";
+		final String r = StrUtil.limitByteLength(s, CharsetUtil.UTF_8, 2, 4, true);
+		assertEquals("ab", r);
+	}
 }