Fixes #4589: Move r31579 to v1.8 branch (bcol/basesmuma: close mmapped file descriptor)

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r31579 [[BR]]
bcol/basesmuma: close mmapped file descriptor

Not closing this file descriptor will cause us to leak file
descriptors. It is safe to close the file after it has been mmapped.

cmr=v1.8.2:reviewer=manjugv