Invalid stack map frames found for MethodAccess subclasses

When instrumenting this example with our agent:

```
package main;

import com.esotericsoftware.reflectasm.MethodAccess;

public class Main {

public static void main(String[] args) {
StringBuilder obj = new StringBuilder("ff");
MethodAccess access = MethodAccess.get(obj.getClass());
System.out.println(access.invoke(obj, "toString"));
}
}
```
I am getting this error when our ASM dependency (6.1.1) tries to parse the generated subclass bytecode `reflectasm/java/lang/StringBuilderMethodAccess`:

```
<< 2018-05-25 10:45:06.643 ERROR 1 Error found instrumenting class reflectasm/java/lang/StringBuilderMethodAccess
<< java.lang.IllegalArgumentException
<< at org.objectweb.asm.ClassReader.readVerificationTypeInfo(ClassReader.java:3138)
<< at org.objectweb.asm.ClassReader.readStackMapFrame(ClassReader.java:3065)
<< at org.objectweb.asm.ClassReader.readCode(ClassReader.java:1812)
<< at org.objectweb.asm.ClassReader.readMethod(ClassReader.java:1238)
<< at org.objectweb.asm.ClassReader.accept(ClassReader.java:631)
<< at org.objectweb.asm.ClassReader.accept(ClassReader.java:355)
<< at io.shiftleft.bctrace.asm.Transformer.transform(Transformer.java:128)
<< at sun.instrument.TransformerManager.transform(TransformerManager.java:188)
<< at sun.instrument.InstrumentationImpl.transform(InstrumentationImpl.java:428)
<< at java.lang.ClassLoader.defineClass1(Native Method)
<< at java.lang.ClassLoader.defineClass(ClassLoader.java:763)
<< at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
<< at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
<< at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
<< at java.lang.reflect.Method.invoke(Method.java:498)
<< at com.esotericsoftware.reflectasm.AccessClassLoader.defineClass(AccessClassLoader.java:85)
<< at com.esotericsoftware.reflectasm.MethodAccess.get(MethodAccess.java:254)
<< at main.Main.main(Main.java:9)
```

After debugging this I see the reason is an [invalid value](https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.4) of 12 (`ITEM_ASM_SHORT`) for a `verification_type_info` of a stack map frame.

I am not sure yet if this is caused by your implementation, or by the ASM dependency your are using, but this bytecode is not valid, and we are suspecting it's one of the reasons for `SIGSEGV` JVM crashes we are experiencing in some environments.