getSvxBrushItemFromSourceSet() is called once for each property of a
frame style that is set, and the "solid" fill-style is set by first
applying the BackColorRGB and then BackTransparency property.  So there
is an intermediate state that has fill-style NONE but a XFillColorItem
set - don't reset the color to white in that case!

Apparently writerfilter generally relies on the current reset-to-AUTO
implementation (loads of test failures), so for now limit the fix for
when we know that a frame style is imported from ODF.

(regression from 3d399b0e)

(cherry picked from commit 79fb61ef)

tdf#92379: sw: unit test for frame style background color

(cherry picked from commit 982537d7)

Change-Id: Ia987fe586ec819a1f3cd85acdbfb03c74ca0ec2c
Reviewed-on: https://gerrit.libreoffice.org/18037Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>