bugfix: setting an element wiped previsouly set attributes

SetElement sets default properties for mass and radius. Previously
set charge and anisou got wiped in the process. Charge and anisou
are now transferred and only mass and radius are reset.

modules/mol/base/src/impl/atom_impl.hh

@@ -116,7 +116,13 @@ public:
   { 
     if (element_!=ele) {
       element_=ele;
+      AtomProp* old_prop = prop_;
       prop_=impl::AtomProp::GetDefaultProps(element_);
+      if (old_prop && !old_prop->is_default) {
+        if(old_prop->has_anisou) this->SetAnisou(old_prop->anisou);
+        if(old_prop->charge != 0.0) this->SetCharge(old_prop->charge);
+        delete old_prop;
+      }
     }
   }
   bool HasDefaultProps() const { return prop_->is_default; }