checking every cell on a sheet is expensive, related fdo#71934

This is only the first of two places that does this.

Change-Id: I57fe1eb07630ecd86b112e88b7ad32c16e9f793a
iterating through all cells is not a good idea, fdo#71934

Change-Id: I370f641f0fffed8835a32c577c2f2e841ba419aa