Fixed default color values for R and RG types

By default, in D3D, R, G or B channels default to 1 when no
value is assigned to them. In OpenGL, these channels default
to 0. Added an entry to Conventions to fix this issue.

In dEQP, this fixes all R and RG types tests from:
functional.texture.format.*

Change-Id: Ib5552aa36eaf4e3e1132f016f002250b40436227
Reviewed-on: https://swiftshader-review.googlesource.com/10828
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/Renderer/Renderer.cpp

diff --git a/src/Renderer/Renderer.cpp b/src/Renderer/Renderer.cpp
index a67ba22..7afbb9f 100644
--- a/src/Renderer/Renderer.cpp
+++ b/src/Renderer/Renderer.cpp
@@ -48,6 +48,7 @@
 	extern bool fullPixelPositionRegister;
 	extern bool leadingVertexFirst;         // Flat shading uses first vertex, else last
 	extern bool secondaryColor;             // Specular lighting is applied after texturing
+	extern bool colorsDefaultToZero;
 
 	extern bool forceWindowed;
 	extern bool complementaryDepthBuffer;
@@ -110,6 +111,7 @@
 		sw::fullPixelPositionRegister = conventions.fullPixelPositionRegister;
 		sw::leadingVertexFirst = conventions.leadingVertexFirst;
 		sw::secondaryColor = conventions.secondaryColor;
+		sw::colorsDefaultToZero = conventions.colorsDefaultToZero;
 		sw::exactColorRounding = exactColorRounding;
 
 		setRenderTarget(0, 0);