[giac] fix for NSolve.2

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25383 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
[giac] updated unit tests

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@25384 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e