Auto resize demo scrolling issue

[maniax89]

Couldn't find an exact issue already opened for this. Things that looked similar included #2368 and potentially when fixing #1514

Basically, if you go to the resize demo http://codemirror.net/demo/resize.html and delete one line and try to scroll using a touchpad or mousewheel inside the codemirror, the numbers and textarea will scroll.

Expected: It shouldn't scroll since no scrollbars are present.

Steps to reproduce:

1. Go to http://codemirror.net/demo/resize.html (has the codemirror height set to auto)
2. Delete a line so that the total number of lines is less than what you started with
3. While focused on the code mirror text area, hover the mouse over that area.
4. Scroll (either using a touch pad or mouse wheel) - content will scroll beyond the visible area

I believe it is due to the height of the gutters being set to be larger than the box itself - but those who have been working on the issue may have better insight to the issue.

I have reproduced this on Mac OSX 10.9.5 on the following browsers:

1. Chrome 43.0.2357.130 (64-bit)
2. Firefox 36.0.1
3. Safari 7.1.3

I also ran Windows 7 on a VM and was able to reproduce it on:

1. IE 9
2. Firefox 38.0.5