do not create a new row, if there is still one empty

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28202 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
patch for corrupted saved files (with an empty cas cell), added exception handling when clickin on empty header,
more consistency between rows (view) and actual GeoCasCell objects (model)


git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28203 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Ticket #3485: CommandDispatcherW is not needed as speedup with that is not easily possible

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@28204 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e