Fix incorrect rgbGen const reading uninitialized memory

If ParseVector fails, color isn't fully set.

code/renderergl1/tr_shader.c

@@ -847,6 +847,8 @@ static qboolean ParseStage( shaderStage_t *stage, char **text )
 			{
 				vec3_t	color;
 
+				VectorClear( color );
+
 				ParseVector( text, 3, color );
 				stage->constantColor[0] = 255 * color[0];
 				stage->constantColor[1] = 255 * color[1];

code/renderergl2/tr_shader.c

@@ -1091,6 +1091,8 @@ static qboolean ParseStage( shaderStage_t *stage, char **text )
 			{
 				vec3_t	color;
 
+				VectorClear( color );
+
 				ParseVector( text, 3, color );
 				stage->constantColor[0] = 255 * color[0];
 				stage->constantColor[1] = 255 * color[1];