Fix for copy action (Ctrl+C) when there is no pager defined in qtconsole

[ccordoba12]

• The absence of a pager was generating an ugly traceback when
  trying to copy text and no pager was created.
• This issue was reported by a Spyder user because all tracebacks
  appear in its internal console, and this one was breaking his workflow.

[ccordoba12]

How to reproduce the bug:

1. Run

ipython qtconsole --paging=none

1. Copy some text
2. You should see this traceback on the terminal:

Traceback (most recent call last):
  File "IPython/frontend/qt/console/console_widget.py", line 331, in eventFilter
    return self._event_filter_console_keypress(event)
  File "IPython/frontend/qt/console/frontend_widget.py", line 302, in _event_filter_console_keypress
    return super(FrontendWidget, self)._event_filter_console_keypress(event)
  File "IPython/frontend/qt/console/console_widget.py", line 1029, in _event_filter_console_keypress
    self.copy()
  File "IPython/frontend/qt/console/frontend_widget.py", line 181, in copy
    if self._page_control.hasFocus():
AttributeError: 'NoneType' object has no attribute 'hasFocus'

[minrk]

Simple enough, thanks!

[ccordoba12]

Ok, thanks! We'll keep you posted (hopefully with more PRs :-) if we find more bugs on our side.