Part: avoid touching in ViewProviderAttachExtension mergeOverlayIcons

ViewProviderAttachExtension::extensionMergeOverlayIcons() calls
AttachExtension::positionBySupport() which will always touch the
extended object. This may cause recomputation problems, e.g a datum
that is always touched, because normal recomputation trigger tree
view update by a timer, tree view refreshes the icon, datum gets
touched again.

src/Mod/Part/Gui/ViewProviderAttachExtension.cpp

@@ -51,16 +51,7 @@ QIcon ViewProviderAttachExtension::extensionMergeOverlayIcons(const QIcon & orig
 
         if (attach) {
 
-            bool attached = false;
-
-            try{
-                attached = attach->positionBySupport();
-            }
-            catch (...) { // We are just trying to get an icon, if no placement can be calculated, set unattached.
-                // set unattached
-            }
-
-            if(!attached) {
+            if(!attach->isAttacherActive()) {
                 QPixmap px;
 
                 static const char * const feature_detached_xpm[]={