r_showLightGrid: fix wrong colors displayed

Sometimes color values were slightly greater than 1; this led to
an incorrect float color -> byte color conversion. Fix it by
clamping the colors in Tess_AddTetrahedron.

Author: slipher

src/engine/renderer/tr_local.h

@@ -3210,7 +3210,7 @@ void GLimp_LogComment_( std::string comment );
 
 	@param tetraVerts[0..2] are the ground vertices, tetraVerts[3] is the pyramid offset
 	*/
-	void Tess_AddTetrahedron( vec4_t tetraVerts[ 4 ], const Color::Color& color );
+	void Tess_AddTetrahedron( vec4_t tetraVerts[ 4 ], Color::Color color );
 
 	void Tess_AddCube( const vec3_t position, const vec3_t minSize, const vec3_t maxSize, const Color::Color& color );
 	void Tess_AddCubeWithNormals( const vec3_t position, const vec3_t minSize, const vec3_t maxSize, const Color::Color& color );

src/engine/renderer/tr_surface.cpp

@@ -399,12 +399,13 @@ void Tess_AddQuadStamp2WithNormals( vec4_t quadVerts[ 4 ], const Color::Color& c
 }
 
 // Defines ATTR_POSITION, ATTR_COLOR
-void Tess_AddTetrahedron( vec4_t tetraVerts[ 4 ], const Color::Color& colorf )
+void Tess_AddTetrahedron( vec4_t tetraVerts[ 4 ], Color::Color colorf )
 {
 	int k;
 
 	Tess_CheckOverflow( 12, 12 );
 
+	colorf.Clamp();
 	Color::Color32Bit color = colorf;
 
 	// ground triangle