[GPU] Handling the case where get_state was called before set_state (o…

…penvinotoolkit#27276)

### Tickets:
 - *[156193](https://jira.devtools.intel.com/browse/CVS-156193)*

src/plugins/intel_gpu/src/plugin/variable_state.cpp

@@ -123,6 +123,12 @@ ov::element::Type VariableState::get_user_specified_type() const {
 }
 
 ov::SoPtr<ov::ITensor> VariableState::get_state() const {
+    if (m_memory == nullptr) {
+        const auto& pshape = m_layout.get_partial_shape();
+        const auto& shape = get_tensor_shape(pshape);
+        return m_context->create_host_tensor(get_user_specified_type(), shape);
+    }
+
     auto tensor = m_context->create_host_tensor(get_user_specified_type(), m_memory->get_layout().get_shape());
 
     convert_and_copy(m_memory, tensor._ptr.get(), m_context->get_engine().get_service_stream());