Assembly: Prevent crash when toggling rigid of grounded sub assembly (#24761)

* Assembly: Prevent crash when toggling rigid of grounded sub assembly

* to squash

* to squash

* Update AssemblyLink.cpp

src/Mod/Assembly/Gui/ViewProviderAssembly.cpp

@@ -628,6 +628,12 @@ bool ViewProviderAssembly::canDragObjectIn3d(App::DocumentObject* obj) const
         return false;
     }
 
+    if (auto* asmLink = dynamic_cast<Assembly::AssemblyLink*>(obj)) {
+        if (!asmLink->isRigid()) {
+            return false;
+        }
+    }
+
     auto* assemblyPart = getObject<AssemblyObject>();
 
     // Check if the selected object is a child of the assembly