IP sometimes not displayed after PageUp or PageDown

[redmunds]

Noticed in Win7. I could not repro this in CodeMirror or brackets-sprint-8.zip.

1. Open brackets/src/thirdparty/jquery-1.7.js
2. Move IP down a few lines using down-arrow key
   >>> Keep track of where Ip is visually in viewport because
   >>> IP should be in same place in viewport after pressing PageDown
3. Press PageDown key
   >>> Sometimes the IP is displayed (blinking), but sometimes it never displays
   >>> To verify IP is where it's supposed to be, hold down shift key and press right-arrow
4. Repeat Add Jasmine unit test framework #3 a dozen or so times
   >>> Not sure of the pattern, but it doesn't display about half the time
   >>> until another key is pressed

Recipe also works in reverse using bottom of page with arrow-up and PageUp keys

Expected Result:
IP should display

[jasonsanjose]

Reproduced on 10.7

[njx]

FBNC to @redmunds -- fix is now in adobe/CodeMirror2 master.

[redmunds]

Confirm fixed.