Keep the standard row height situation under control.

With this change, applying cell attributes to default cells will
no longer change the row heights inadvertently.

Without this, applying background colors to cells, pasting to a 
range of cells etc would make the row heights slightly shorter 
which is 1) odd, and 2) causes all sorts of rendering issues because 
internally we assume these actions wouldn't change the row heights.

Change-Id: I57c3546e1725c5e8b37696242e9642b1617f59c3
(cherry picked from commit 29b322ea0c40423a39efe2f6c2c85a7d2108c512)
Reviewed-on: https://gerrit.libreoffice.org/7774
Reviewed-by: Fridrich Strba <fridrich@documentfoundation.org>
Tested-by: Fridrich Strba <fridrich@documentfoundation.org>