Fix wrong GL DepthTest param

[Helwor]

That may disturb other widgets (especially Eco Drawer).

[GoogleFrog]

Have you checked whether the widget that runs after this one (by default) happens to rely on this state being left there?

[GoogleFrog]

I ask because either you've tested it, or I am going to have to.

[sprunk]

widget:DrawGroundDeferred() doesn't seem to be a real thing. Maybe it's BAR specific?

The full list of widgets using widget:DrawWorldPreUnit() after enabling this one:

Mex Placement Handler
Custom Markers
Lups
AllyCursors
Map Edge Extension
Commands FX
Map Edge Extension 2        <----
Showeco and Grid Drawer
Missile Impact Points
Defense Range Zero-K
Decloak Range
Antinuke Coverage
Selected Units GL4 2
API Unit Tracker GL4

It looks like lots of things below and above happens to rely on whatever state they inherit from the previous widget. I put a little test on the glDepthTest-debug branch and at least defense ranges, antinuke ranges, mex spots, and OD pylon circles get broken in various ways if they start with the wrong glDepthTest value.