Objects are not rendered when camera is looking straight down

When camera is pointing straight down (i.e. camera's and view center's positions on X and Z axis are the same while Y is different) objects are not rendered at all. Changing the Y value does not seem change anything.

The example provided will move camera and view center on Z axis and offsets camera position before restarting the movement. The camera starts at +1 offset.

Steps to reproduce:
1. Compile and run the example
-> Watch the positions of camera and view center. When both are identical, nothing is rendered.