initialize hlen_b4_cell also in the no readline case

IPython/frontend/terminal/interactiveshell.py

@@ -275,6 +275,8 b' class TerminalInteractiveShell(InteractiveShell):'
         if self.has_readline:
             self.readline_startup_hook(self.pre_readline)
             hlen_b4_cell = self.readline.get_current_history_length()
+        else:
+            hlen_b4_cell = 0
         # exit_now is set by a call to %Exit or %Quit, through the
         # ask_exit callback.