Prevent division by 0 error in ScreenSpaceSkybrowser (closes #3696)

src/rendering/screenspacerenderable.cpp

@@ -740,7 +740,7 @@ glm::vec3 ScreenSpaceRenderable::cartesianToSpherical(const glm::vec3& cartesian
     const float r = std::sqrt(
         std::pow(rotated.x, 2.f) + std::pow(rotated.y, 2.f) + std::pow(rotated.z, 2.f)
     );
-    const float theta = std::acos(rotated.z / r);
+    const float theta = std::acos(r != 0.f ? rotated.z / r : rotated.z);
     const float phi = std::atan2(rotated.y, rotated.x);
     return sanitizeSphericalCoordinates(glm::vec3(r, theta, phi));
 }