Concat Squeeze Fix (adressing SEEFO pipe error)

When using squeeze option for history concatenation, the squeezed history (as a result of history.max) will evaluate to UNFLAGGED constant, where the input history was all UNTOUCHED - this leads to shadowing flags in the history, the squeezed history gets appended to. This leads to flag loss.

The fix just stores a mask and regains UNFLAGGED values after squeezing with history.max in concatFlags