Fixing the -1 detection bug in Botana's prover NDGs

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26822 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
enable/disable buttons (save, redo, undo)

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@26823 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e