Missing input validation can cause memory corruption.

I have some code that can vary the batch size as I process the data. I have been trying it with mxnet, and ran into memory corruptions and crashes. I traced the problem to an wrongly sized array, code to reproduce the problem is attached. Ideally mxnet should report the array is of an unexpected size and abort.

[testMXNet.zip](https://github.com/dmlc/MXNet.cpp/files/777305/testMXNet.zip)

Start by running the attached testMXNet.zip reproduction and trace the wrongly sized array through the MXNet C++ interface. Identify where the batch-size input is accepted and determine how an unexpected array size is currently handled. Done means the invalid size is reported and processing aborts without memory corruption or a crash.

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