Fix glu::FboRenderContext
Fix glu::FboRenderContext

FboRenderContext was always crashing since it was attempting to query
bit depth for combined depth stencil formats.

Change-Id: I986e228c22fe36b799756ddf24a192456c1eea69

KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/Vulkan-CTS,googlestadia/VK-GL-CTS,KhronosGroup/VK-GL-CTS,googlestadia/VK-GL-CTS,chadversary/deqp,KhronosGroup/VK-GL-CTS,googlestadia/VK-GL-CTS,chadversary/deqp,KhronosGroup/VK-GL-CTS,chadversary/deqp,KhronosGroup/Vulkan-CTS,chadversary/deqp,googlestadia/VK-GL-CTS,chadversary/deqp,KhronosGroup/VK-GL-CTS,KhronosGroup/VK-GL-CTS,chadversary/deqp,KhronosGroup/Vulkan-CTS,googlestadia/VK-GL-CTS,googlestadia/VK-GL-CTS,KhronosGroup/Vulkan-CTS,KhronosGroup/VK-GL-CTS