Some defensive coding

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@34135 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Some defensive coding

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@34136 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e