fdo#73080: Write test for this first.

Change-Id: Ia2a32f4be3ef2c09ac68fe03ee9a7c9d31aef7ed
fdo#73080: Correctly count blank cells in COUNTBLANK.

Especially when formula cells are involved.

Change-Id: I40950e7108778821c17d08354f01bb157b1551e6