Fix checkfail in raw_ops.DenseBincount
This seems reasonable to me, but I'll let @cantonios to give final approval. Thanks for doing these fixes!
The API `raw_ops.DenseBincount` lacks validation of input to be vector. It does have checking for rank<=2 but not check for rank>0. Passing a scalar value causes checkfail with debug build.

Reported at #63068