fix line bug

hutool-core/src/main/java/cn/hutool/core/io/file/LineReadWatcher.java

@@ -50,11 +50,11 @@ public class LineReadWatcher extends SimpleWatcher implements Runnable {
 		try {
 			final long currentLength = randomAccessFile.length();
 			final long position = randomAccessFile.getFilePointer();
-			if (0 == currentLength || position == currentLength) {
+			if (position == currentLength) {
 				// 内容长度不变时忽略此次事件
 				return;
 			} else if (currentLength < position) {
-				// 如果内容变短，说明文件做了删改，回到内容末尾
+				// 如果内容变短或变0，说明文件做了删改或清空，回到内容末尾或0
 				randomAccessFile.seek(currentLength);
 				return;
 			}

hutool-core/src/test/java/cn/hutool/core/io/file/TailerTest.java

@@ -7,13 +7,13 @@ import cn.hutool.core.io.FileUtil;
 import cn.hutool.core.util.CharsetUtil;
 
 public class TailerTest {
-	
+
 	@Test
 	@Ignore
 	public void tailTest() {
-		FileUtil.tail(FileUtil.file("e:/tail.txt"), CharsetUtil.CHARSET_GBK);
+		FileUtil.tail(FileUtil.file("d:/test/tail.txt"), CharsetUtil.CHARSET_GBK);
 	}
-	
+
 	@Test
 	@Ignore
 	public void tailWithLinesTest() {