[giac] adding caseval back for initString (needed for giac.js)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29617 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
updated CAS test-case for #3752 x<1 && x<2

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@29618 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e