tdf#148819: let the scroller know the custom widget's line size

Change-Id: Ie30cd1db182aad5fbbf7e89498bd0ae9ce98c0f3
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/133518
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>
diff --git a/starmath/source/ElementsDockingWindow.cxx b/starmath/source/ElementsDockingWindow.cxx
index 7f1b861..ed67baa 100644
--- a/starmath/source/ElementsDockingWindow.cxx
+++ b/starmath/source/ElementsDockingWindow.cxx
@@ -500,6 +500,7 @@ void SmElementsControl::LayoutOrPaintContents(vcl::RenderContext& rContext, bool
            mxScroll->hadjustment_set_upper(nTotalControlWidth);
            mxScroll->hadjustment_set_page_size(nControlWidth);
            mxScroll->hadjustment_set_page_increment(nControlWidth);
            mxScroll->hadjustment_set_step_increment(boxX);
            mxScroll->set_hpolicy(VclPolicyType::ALWAYS);
        }
        else
@@ -516,6 +517,7 @@ void SmElementsControl::LayoutOrPaintContents(vcl::RenderContext& rContext, bool
            mxScroll->vadjustment_set_upper(nTotalControlHeight);
            mxScroll->vadjustment_set_page_size(nControlHeight);
            mxScroll->vadjustment_set_page_increment(nControlHeight);
            mxScroll->vadjustment_set_step_increment(boxY);
            mxScroll->set_vpolicy(VclPolicyType::ALWAYS);
        }
        else