#3977: [desktop] Offline mode without login and OpenFromGGT - The check if tube is available is performed in an own thread now to avoid delays on startup

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31071 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e
Fix for #3958

git-svn-id: http://dev.geogebra.org/svn/trunk/geogebra@31072 23ce0884-8a58-47d3-bc5c-ddf1cd5b9f9e