[giac] updated unit tests

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25172 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Quick fix for NPE (grid + axes now drawn, but without white rectangles to make the numbers more visible)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25173 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e