3D Map broken after version 1.3.68

#### Issue details
3D Map works fine with 1.3.68.

With 1.3.69 however, the ground is very blurry, and with 1.3.71 it basically stopped working: the ground is either all black or blue. I tried adjusting the two numbers in the top left corner (no idea what they are) and enable/disable fog and "lock to mav" but that doesn't help.

#### Version
See above.

#### Platform
[X] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[ ] Sub

The report names no files, tests, or entry points, so begin by reproducing the 3D Map behavior in Mission Planner versions 1.3.68, 1.3.69, and 1.3.71 while checking the fog, lock-to-MAV, and top-left settings. Trace the 3D Map rendering path to identify the regression; done means the ground renders correctly rather than appearing blurry, black, or blue.

Written by the indexing model from the issue text.