!6693 [MS][LITE][GPU]fix bug: run model shutdown

Merge pull request !6693 from chenzupeng/master-lite-2

mindspore/lite/src/runtime/kernel/opencl/subgraph_opencl_kernel.cc

@@ -321,6 +321,10 @@ int SubGraphOpenCLKernel::ReSize() { return RET_OK; }
 
 int SubGraphOpenCLKernel::Run() {
   for (auto &tensor : in_tensors_) {
+    if (tensor->data_c() == nullptr) {
+      MS_LOG(ERROR) << "OpenCL subgraph input tensor data is null";
+      return RET_ERROR;
+    }
     allocator_->UnmapBuffer(tensor->data_c());
   }