Add case to handle 0-D vectors in...

Add case to handle 0-D vectors in FlattenContiguousRowMajorTransferWritePattern and FlattenContiguousRowMajorTransferReadPattern.

For 0-D as well as 1-D vectors, both these patterns should
return a failure as there is no need to collapse the shape
of the source. Currently, only 1-D vectors were handled. This
patch handles the 0-D case as well.

Reviewed By: Benoit, ThomasRaoux

Differential Revision: https://reviews.llvm.org/D119202