ILGenerator.BeginFinallyBlock example is invalid

As discovered by @luboid in https://github.com/dotnet/coreclr/issues/14379#issuecomment-334959413, [the example code for `ILGenerator.BeginFinallyBlock`](https://docs.microsoft.com/en-us/dotnet/api/system.reflection.emit.ilgenerator.beginfinallyblock?view=netcore-2.0#Examples) contains branch out of try block and is thus invalid. When I run it on .Net Framework 4.7 in x64 mode or .Net Core 2.0 (after changing `myAppDomain.DefineDynamicAssembly` to `AssemblyBuilder.DefineDynamicAssembly` and removing the permissions attribute to make it compile on .Net Core 2.0), I get the following exception:

```
Unhandled Exception: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidProgramException: Common Language Runtime detected an invalid program.
at Adder.DoAdd(Int32 , Int32 )
--- End of inner exception stack trace ---
at System.RuntimeMethodHandle.InvokeMethod(Object target, Object[] arguments, Signature sig, Boolean constructor)
at System.Reflection.RuntimeMethodInfo.UnsafeInvokeInternal(Object obj, Object[] parameters, Object[] arguments)
at System.RuntimeType.InvokeMember(String name, BindingFlags bindingFlags, Binder binder, Object target, Object[] providedArgs, ParameterModifier[] modifiers, CultureInfo culture, String[] namedParams)
at System.Type.InvokeMember(String name, BindingFlags invokeAttr, Binder binder, Object target, Object[] args)
at ILGenerator_BeginFinallyBlock.Main() in C:\code\tmp\coreapp\Program.cs:line 109
```

I think the example should be changed, so that it produces valid IL.