Contour layer is overflowed with red color on Mac devices

[altgov3en]

I have an app which facilitates Cornerstone API (ver. 2.2.8) to render Contour image over an NM image (2 layers).

Everything works flawlessly on Windows devices (Chrome and Firefox) but there is an edge cases on Mac devices (Safari and Chrome as well) where one of the images is shown as a red rectangle.

At first, I thought, may be it related to color-map I've defined for Contour images, but after removing the color-map definition (the Contour image still exists but invisible) the issue has still remained.

[tapin13]

Fix #572