Preselection is sometimes not updated under some circumstances
1. when deleting an object through python;
2. before autoconstraint when deleting previous pole in bspline creation mode.
When the preselected curve is the deleted object, segfault/crash can happen.
If package.xml metadata file exists, it is scanned for FreeCAD version
compatibility before the Addon is loaded. If the Addon specifies that it is
explicitly not compatible with the current version of FreeCAD, the Addon is
not loaded.