Switch the parameter from a pointer to a reference.
The only 2 callers in SfxChildWindow::CreateChildWindow
always pass a non-null param.
Using a reference makes clear that the param is always
non-null and makes clear that those implementations previously
unconditionally dereferencing the pointer were unproblematic.
Change-Id: Ia2b893aac6c94c3b0e1024cc5500da2463bf9996
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/208312
Reviewed-by: Michael Weghorn <m.weghorn@posteo.de>
Tested-by: Jenkins