Set general global handle for extension registration work

* When calling the register() function there is no frame or globals, so we need
  to set an internal handle external to that.
* This means functions that get wrapped know that there's a global handler for
  exceptions, which just prints to the log. Otherwise they think they're running
  synchronously and write to an invalid exception handling object.

qrenderdoc/Code/pyrenderdoc/pyrenderdoc_stub.cpp

@@ -46,6 +46,11 @@ extern "C" PyThreadState *GetExecutingThreadState(PyObject *global_handle)
   return NULL;
 }
 
+extern "C" PyObject *GetCurrentGlobalHandle()
+{
+  return NULL;
+}
+
 extern "C" void HandleException(PyObject *global_handle)
 {
 }