ASSERTION (pFuncBody->GetYieldRegister() == oldYieldRegister) failed in Js::DebugContext::RundownSourcesAndReparse

###### ChakraCore version:
version 1.12.0.0-beta

###### Build Commond
./build.sh --debug

###### OS
Ubuntu 16.04.6 LTS (Linux 4.4.0-142-generic x86_64)

###### Test case
```
function test0() {
var func2 = (async (xsbazt = hkvvxr(x)) => [...[
-2,
]]);
var a = -191;
func3(a);
}

function Run(){
WScript.Echo('PASSED');
}

WScript.Attach(Run);
```

###### Output
```
ASSERTION 202914: (ChakraCore/lib/Runtime/Debug/DebugContext.cpp, line 359) pFuncBody->GetYieldRegister() == oldYieldRegister
Failure: (pFuncBody->GetYieldRegister() == oldYieldRegister)
Illegal instruction
```

Credits: This vulnerability is detected by chong from OWL337.