Do not try to paste empty clipboard as row

Closes #13613

tryton/tryton/gui/window/view_form/view/list.py

@@ -785,6 +785,8 @@ class ViewTree(View):
                 continue
             reader = csv.reader(StringIO(text), delimiter='\t')
             break
+        else:
+            return
         col = self.treeview.get_cursor()[1]
         columns = [c for c in self.treeview.get_columns()
             if c.get_visible() and c.name]