Execute body of host_task if main interpreter is still initialized (#776)

Author: oleksandr-pavlyk

dpctl/_host_task_util.hpp

@@ -55,7 +55,8 @@ int async_dec_ref(DPCTLSyclQueueRef QRef,
                     *(reinterpret_cast<sycl::event *>(ERefs[ev_id])));
             }
             cgh.host_task([obj_array_size, obj_vec]() {
-                {
+                // if the main thread has not finilized the interpreter yet
+                if (Py_IsInitialized()) {
                     PyGILState_STATE gstate;
                     gstate = PyGILState_Ensure();
                     for (size_t i = 0; i < obj_array_size; ++i) {