filtered observation must be unboxed for completing missing data

[dtolpin]

Unless unboxed, a single element matrix is inserted into the data, and autoReg component fails. Unit test modified so that it manifests the error without the change.

[coveralls]

Coverage remained the same at 76.1% when pulling 53c344d8f09b90686913549c1a0107814d803508 on dtolpin:unbox-missing into a2ea2eab4e59f75ba719d537cf60bb3eb3080896 on wwrechard:master.