Use a equal operator that don't depend on nonzero for flatbuffer_serializer (#97298)
Summary: call to is_nonzero here is not desirable: https://www.internalfb.com/code/fbsource/[ed0407ba3bf520baa2e9333483b274c5b40b54eb]/fbcode/caffe2/aten/src/ATen/core/ivalue.cpp?lines=278
Differential Revision: D44276685
Pull Request resolved: https://github.com/pytorch/pytorch/pull/97298
Approved by: https://github.com/larryliu0820
