This commit try to avoid this crash, but without any certitude because the crash is very difficult to reproduce
git-svn-id: svn+ssh://svn.tuxfamily.org/svnroot/qet/qet/trunk@4959 bfdf4180-ca20-0410-9c96-a3a8aa849046
Drag & drop an element in a diagram and click left to add it, click right to finish
git-svn-id: svn+ssh://svn.tuxfamily.org/svnroot/qet/qet/trunk@3803 bfdf4180-ca20-0410-9c96-a3a8aa849046