Solve  when terminal window size is 80 * 24 press "h" error bug

When I useGlances. I found that when clicking 'h' that you want to display help information will displayer error（a part）:

```
self.displayHelp(core=stats.getCore())
File "/usr/lib64/python2.7/site-packages/Glances-1.7a-py2.7.egg/glances/glances.py", line 3187, in displayHelp
'{0:{width}}{1}'.format(*key, width=width), 38)
_curses.error: addnstr() returned ERR
```

I modified the source code for this situation made ​​a judgment, and then remove the spacer block above them .... I do not know there is no better way to achieve