createDepthStencilSurface stencil fix

Stencil formats were prohibited from createDepthStencilSurface
in debug builds due to an assert, so fixed the assert.

Change-Id: I5777a081371be4f43810de4450b415c55f04a8d7
Reviewed-on: https://swiftshader-review.googlesource.com/16348
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
diff --git a/src/OpenGL/libGLESv2/Device.cpp b/src/OpenGL/libGLESv2/Device.cpp
index 6724976..e82b252 100644
--- a/src/OpenGL/libGLESv2/Device.cpp
+++ b/src/OpenGL/libGLESv2/Device.cpp
@@ -251,7 +251,7 @@
 
 	egl::Image *Device::createDepthStencilSurface(unsigned int width, unsigned int height, sw::Format format, int multiSampleDepth, bool discard)
 	{
-		ASSERT(sw::Surface::isDepth(format));
+		ASSERT(sw::Surface::isDepth(format) || sw::Surface::isStencil(format));
 
 		if(height > OUTLINE_RESOLUTION)
 		{