[giac] attempt to catch factorization error in sqrt for #4611

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36819 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
#4557 - 0 and + buttons work

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@36820 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e