When moving back a row that has a single text frame, it should not
matter if that text frame is in a section frame or not.

The problem was that the bugdoc has a split (outer) table, the follow's
ShouldBwdMoved() returned false, as
SwTabFrame::CalcHeightOfFirstContentLine() returned USHRT_MAX, as it had
no idea how to calc the height of a text frame in a section frame.

Fix this by looking "through" the section frame, and handling "text
frame" and "text frame in section frame" the same way.

Change-Id: Ic3605a1e2d28bfaa69bf18f31cfbf1e6e681c04f
Reviewed-on: https://gerrit.libreoffice.org/44393Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>