-        This->txtSel->reOle = NULL;
-        ITextSelection_Release(&This->txtSel->ITextSelection_iface);
-        IOleClientSite_Release(&This->clientSite->IOleClientSite_iface);
+        if(This->txtSel)
+          {
+            This->txtSel->reOle = NULL;
+            ITextSelection_Release(&This->txtSel->ITextSelection_iface);
+          }
+        if(This->clientSite)
+          {
+            This->clientSite->reOle = NULL;
+            IOleClientSite_Release(&This->clientSite->IOleClientSite_iface);
+          }
          heap_fr

This can't happen.

      IOleClientSiteImpl *This = impl_from_IOleClientSite(iface);
      ULONG ref = InterlockedDecrement(&This->ref);
      if (ref == 0)
+      {
+        if(This->reOle)
+          This->reOle->clientSite = NULL;
          heap_free(This);
+      }
      return ref;

Why do you need this?