fix crash on Java 8 (#1954)

HMCL/src/main/java/org/jackhuang/hmcl/upgrade/ExecutableHeaderHelper.java

@@ -19,6 +19,7 @@ package org.jackhuang.hmcl.upgrade;
 
 import java.io.IOException;
 import java.io.InputStream;
+import java.nio.Buffer;
 import java.nio.ByteBuffer;
 import java.nio.channels.FileChannel;
 import java.nio.channels.FileChannel.MapMode;
@@ -75,7 +76,7 @@ final class ExecutableHeaderHelper {
         suffixLoop: for (String suffix : suffix2header.keySet()) {
             Optional<byte[]> header = readHeader(zip, suffix);
             if (header.isPresent()) {
-                buf.rewind();
+                ((Buffer) buf).rewind();
                 for (byte b : header.get()) {
                     if (!buf.hasRemaining() || b != buf.get()) {
                         continue suffixLoop;