For a block invoke to another thread, safe and restore

* In future we could handle async exceptions by storing the exception
  information in a std::function derived object (instead of the separate
  ExceptionHandling that lives on the stack) and query it out in a new
  WaitForInvoke function maybe. Right now we just print the exception
  to the output log and abort the callback.

qrenderdoc/Code/pyrenderdoc/pyrenderdoc_stub.cpp

@@ -32,3 +32,12 @@ extern "C" PyThreadState *GetExecutingThreadState(PyObject *global_handle)
 extern "C" void HandleException(PyObject *global_handle)
 {
 }
+
+extern "C" bool IsThreadBlocking(PyObject *global_handle)
+{
+  return false;
+}
+
+extern "C" void SetThreadBlocking(PyObject *global_handle, bool block)
+{
+}