handle NDArray slice properly for mkldnn layout

[ashokei]

Description

when NDArray asnumpy is called for a view of NDArray, and if the original NDArray has mkldnn layout, a crash is seen. Below code snippet reproduces this issue.

ctx = mx.cpu()
net = gluon.nn.HybridSequential()
with net.name_scope():
    net.add(gluon.nn.Conv2D(channels=32, kernel_size=3, activation=None))
net.collect_params().initialize(mx.init.Xavier(magnitude=2.24), ctx=ctx)
x=nd.array(np.ones([32,3,224,224]), ctx)
y=net(x)

# no issue seen for below
#z=y.asnumpy()

# crash seen for below
z=y[0].asnumpy()

print(z[0,0,0])

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [MXNET-$JIRA_ID], where $JIRA_ID refers to the relevant JIRA issue created (except PRs with tiny changes)
• Changes are complete (i.e. I finished coding on this PR)
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• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
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• For user-facing API changes, API doc string has been updated.
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• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

Changes

• Feature1, tests, (and when applicable, API doc)
• Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

[ashokei]

@zheng-da please review, thanks.

[zheng-da]

can you also add the code snippet as a test?

[ashokei]

@zheng-da can you please review and accept PR, unittest is added. please add approver also, thanks.

[ashokei]

@zheng-da @piiswrong can you please merge this if ok, thanks.