使用Bytekit 做Agent 对所有类做增强时，会出现`duplicate class definition`的错误

环境： Windows 10 64 bit/Oracle JDK8

问题复现的demo（必现问题） -> https://github.com/kongwu-/bytekit-agent-sample

Transform类很简单，什么增强内容都没做，只是调用了一下AsmUtils.toClassNode

```java
public class SmpClassTransformer implements ClassFileTransformer {
@Override
public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
System.out.println("enhance... "+className);
try {
ClassNode classNode = AsmUtils.toClassNode(classfileBuffer);

// 获取增强后的字节码

// 打印ClassLoader 日志之后，发现这里会进行Class load，而且ClassLoader是Launcher$AppClassLoader
// 这个toBytes 会 load class 有点不太理解，只是生成字节码需要 define 一次嘛……
byte[] bytes = AsmUtils.toBytes(classNode);
//transformer 返回后，会再次打印一遍Class Load日志，ClassLoader 仍然是 Launcher$AppClassLoader
return bytes;
}catch (Error e){
e.printStackTrace();
return classfileBuffer;
}
}
```

最后打包 Agent 运行时，就会出现重复定义类的错误：`loader (instance of sun/misc/Launcher$AppClassLoader): attempted duplicate class definition for name: "org/springframework/core/NestedRuntimeException"`（理论上很多类都会出现这个问题，只是碰巧报错的是Spring的）。

transform 方法中load 了两遍，也没报错，这里应该算是第三遍load了，此时发生错误：duplicate class definition

stack trace 也有一点奇怪：

```
Exception in thread "main" java.lang.LinkageError: loader (instance of sun/misc/Launcher$AppClassLoader): attempted duplicate class definition for name: "org/springframework/core/NestedRuntimeException"

at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)

//native define Class 之后，又调用 loadClass
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:756)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:468)
at java.net.URLClassLoader.access$100(URLClassLoader.java:74)
at java.net.URLClassLoader$1.run(URLClassLoader.java:369)
at java.net.URLClassLoader$1.run(URLClassLoader.java:363)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:362)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:352)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at org.example.App.main(App.java:13)
```

按道理说，同一个ClassLoader，define一次之后就被缓存了，再次loadClass时就会从缓存中获取了，这里报错实在想不通。

Reproduce the issue with the bytekit-agent-sample on Windows 10 and Oracle JDK8, starting from SmpClassTransformer.transform and the AsmUtils.toClassNode/toBytes calls. Trace the class-loading sequence through org.example.App.main at App.java:13 and the reported AppClassLoader stack. Done means identifying why duplicate definition occurs and documenting or validating a fix for the repeated loading path.

Written by the indexing model from the issue text.