Prevent crashes when loading tensor slices with unsupported types.

[pranve]

Also fix the Tensor(const TensorShape&) constructor swapping the LOG(FATAL)
messages for the unset and unsupported types.

PiperOrigin-RevId: 392695027
Change-Id: I4beda7db950db951d273e3259a7c8534ece49354
(cherry picked from commit abcced0)

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[gbaned]

@pranve Can you please sign CLA. Thanks!

[pranve]

@googlebot I signed it!