If panel's requested minimal size is smaller than current sidebar width,
enlarge the sidebar to fit the content.

Change-Id: I9baa4ef6c01d5563951d4df0d939883fce02e87b
Reviewed-on: https://gerrit.libreoffice.org/69561
Tested-by: Jenkins
Reviewed-by: Samuel Mehrbrodt <Samuel.Mehrbrodt@cib.de>