Running out of suggestions causes awesome bar to stop suggesting about tenfourfox HOT 7 CLOSED

This is somewhat mitigated with large histories, obviously. New windows and 
tabs fix the problem.

The awesome bar appears to still be here and still gets events. You can TAB to 
(invisible) suggestions, and you can use arrow keys. Perhaps it's not that the 
awesome bar is invisible but that it's behind the window it's attached to.

However, other things that make the awesome bar drop down disappear allow it to 
come back later, so there must be something specific about underflowing the 
result.

Things that it is not:

- It is not due to our fix for issue 9 (backing that out made no difference)

- It is not due to ClosePopup() in 
toolkit/components/autocomplete/src/nsAutoCompleteController.cpp (making the 
function return NS_OK made no difference; the popup still closed)

Currently homing in on toolkit/content/widgets/autocomplete.xml ...

Making the changes to the autocomplete widget had unexpected side effects. So 
we took a different tack.

The only time that the awesome bar goes bad is when it runs out of suggestions 
-- other things that close it work (for reasons unclear to me). Since I'm not 
sure how to fix that, the other solution is ... never let it run out of 
suggestions. If toolkit/components/places/src/nsPlacesAutoComplete.js finds 
that no matches are returned, it makes a bogus placeholder that is blank, so it 
just looks like a blank dropdown. This is totally shippable, and totally works 
-- the awesomebar now functions otherwise normally.

Until I figure out how to get rid of that, this is an acceptable compromise (so 
issues complaining about the blank Awesome bar will be wontfixed unless the 
real cause is discovered). This has no other side effects, so this is now 
Verified.

Side-effect alert:

This breaks at least the Omnibar and Cybersearch plugins and possibly many 
others, causing them to delete the contents of the URL bar whenever the blank 
placeholder would normally appear, it took me a while to correlate it to this 
bugfix. 

In addition to causing extension problems, I'm thinking this bugfix might be 
problematic when Mozilla retires the search box, as it seems to interfere with 
anything wanting to serve up search suggestions in the awesome bar.

Please post the screenshot I asked for in the tenderapp ticket; I'm already 
aware of the issue.