gl-renderer: color transform output borders

Use the sRGB to output color space transformation when blitting the
borders (decorations) into an output window (nested compositor).

Nested output does not need to be sRGB anymore, as far as the
decorations are concerned.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

libweston/renderer-gl/gl-renderer.c

@@ -1294,7 +1294,6 @@ draw_output_borders(struct weston_output *output,
 		.req = {
 			.variant = SHADER_VARIANT_RGBA,
 			.input_is_premult = true,
-			.color_pre_curve = SHADER_COLOR_CURVE_IDENTITY,
 		},
 		.view_alpha = 1.0f,
 	};
@@ -1306,7 +1305,10 @@ draw_output_borders(struct weston_output *output,
 	if (border_status == BORDER_STATUS_CLEAN)
 		return; /* Clean. Nothing to do. */
 
-	assert(output->from_sRGB_to_output == NULL);
+	if (!gl_shader_config_set_color_transform(&sconf, output->from_sRGB_to_output)) {
+		weston_log("GL-renderer: %s failed to generate a color transformation.\n", __func__);
+		return;
+	}
 
 	top = &go->borders[GL_RENDERER_BORDER_TOP];
 	bottom = &go->borders[GL_RENDERER_BORDER_BOTTOM];