修复isDir判断改变pwd的问题

hutool-extra/src/main/java/cn/hutool/extra/ftp/AbstractFtp.java

@@ -73,7 +73,12 @@ public abstract class AbstractFtp implements Closeable {
 	 * @since 5.7.5
 	 */
 	public boolean isDir(String dir) {
-		return cd(dir);
+		final String workDir = pwd();
+		try {
+			return cd(dir);
+		} finally {
+			cd(workDir);
+		}
 	}
 
 	/**

hutool-extra/src/test/java/cn/hutool/extra/ftp/FtpTest.java

@@ -90,4 +90,14 @@ public class FtpTest {
 					FileUtil.file("d:/test/download/" + name));
 		}
 	}
+
+	@Test
+	@Ignore
+	public void isDirTest() throws Exception {
+		try (Ftp ftp = new Ftp("127.0.0.1", 21)) {
+			Console.log(ftp.pwd());
+			ftp.isDir("/test");
+			Console.log(ftp.pwd());
+		}
+	}
 }