Scrolling in the ColorBar and minor fixes

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23751 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
possible nullpointer exception averted

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@23752 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e