QTConsole Fix calltip widget y-padding

![shot](https://cloud.githubusercontent.com/assets/7333933/4716296/d5d5cf8a-5906-11e4-8852-863b630e2432.png)

See how [L159/160](https://github.com/kalibri1798/ipython/blob/9ee4e4c16f3b6772238c2d87170a73a60b484b45/IPython/qt/console/call_tip_widget.py#L159 )  also applies padding unconditionally, I restored that logic so it applies whether the `if` is taken or not.

Closes #6756