[Sketcher] Fix crash in SketcherObject::setDatum

The variable newVals can't be used after std::move, fetch it from the
constraint it if an error occurs.

src/Mod/Sketcher/App/SketchObject.cpp

@@ -362,7 +362,7 @@ int SketchObject::setDatum(int ConstrId, double Datum)
     int err = solve();
 
     if (err)
-        newVals[ConstrId]->setValue(oldDatum);
+        this->Constraints.getValues()[ConstrId]->setValue(oldDatum); // newVals is a shell now
 
     return err;
 }