Fix squeeze and concat when all tensors are 0 sized

[dsmilkov]

• Make sure squeeze() on zero-sized tensors works.
• Make sure concat(inputs) where all inputs are zero-sized works.

Both changes are motivated by bugs showing up on ssd_mobilenet_v2_coco

BUG

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This change is 

[nsthorat]

Reviewed 8 of 8 files at r1.
Reviewable status: 0 of 1 approvals obtained (waiting on @dsmilkov, @nsthorat, and @pyu10055)

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src/tensor_test.ts, line 945 at r1 (raw file):

    const a = tf.tensor3d([], [0, 1, 0]);
    const res = tf.squeeze(a);
    expect(res.shape).toEqual([0, 0]);

this is so weird lol

[pyu10055]

Reviewed 8 of 8 files at r1.
Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov and @pyu10055)

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src/ops/concat_util.ts, line 42 at r1 (raw file):

export function computeOutShape(shapes: number[][], axis: number): number[] {
  const outputShape = shapes[0].slice();

do you need to make sure the shapes have the same rank?

[dsmilkov]

Reviewable status: complete! 1 of 1 approvals obtained (waiting on @dsmilkov)

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src/tensor_test.ts, line 945 at r1 (raw file):

Previously, nsthorat (Nikhil Thorat) wrote…

this is so weird lol

I know.. but caused exception on coco_ssd model, so we have to fix it :)

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src/ops/concat_util.ts, line 42 at r1 (raw file):

Previously, pyu10055 (Ping Yu) wrote…

do you need to make sure the shapes have the same rank?

The check I removed was redundant since the assertParams() method above does the validation, which we call before we call this method.

[pyu10055]

Reviewable status: complete! 1 of 1 approvals obtained