Fixed NPE on properties loading

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25408 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Thai: Rachaya Srisurichan

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25412 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fix for command and tool tangent of CubicSpline if point is undefined/infinite or list is empty

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25413 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e