Fix dangling popup

[yshavit]

If a sheet opens up over the popup, and then someone asks the autoresponder to become the first responder (as PTN does, within the grabFocusNow() it calls on open), the popup pops through the sheet. This looks really bad. So, fix it.

Manual tests:

• PTN opens with a sheet
  1. start up whatdid in UI test mode
  2. set the time to 60000
  3. PTN will open with a "it's been a while" sheet; confirm no popup
• PTN is already open
  1. start up whatdid in UI test mode
  2. open up the PTN
  3. set the time to 60000, but using the delayed timer (hold ⇧shift while pressing enter)
  4. before the timer expires, open one of the autocomplete popups
  5. it should close when the PTN opens