Correct broken rotated or course up display in single chart DC mode.

The problems only occurred without opengl, in single chart mode.

First commit corrects the use of the rotated cache (fixes the display turning gray because of incorrect use of temp_dc)

The reverted commit is needed because it doesn't correctly calculate the chart coordinates.

The problem is very easily reproduced by rotating the chart (with [ and ]) in single chart mode when the world background chart is also visible on part of the screen (single chart doesn't cover entire viewport)