Related: fdo#65634 make sidebar react to resizes when floating

the parent isn't a SfxSplitWindow in this case, but it should
still react to the resize

Change-Id: Ia298d45b33fc272d6169df12cf2c58a881255163
(cherry picked from commit df630b8f8c2c92ec2cd1e4be6a3f54a4e4960e92)