See Issue #2443.
When there's more than 2 rectangles in the region structure, region16_intersect_rect would calculate extents by all 'intersected' sub rectangles.
But it always extend the extents to (0,0) because it initialize the new extents as (0,0,0,0) and union later rectangles with this empty point by simple MIN/MAX calculation.
Also fixed rectangle_is_empty although it has not been used yet. The function does not work as its name.
Reuse norbert case. That case is enough for the intersect fix, but the expected result is not correct. The test case is also fixed.
Added test case to check empty rectangle.
f94935224c