gl-renderer: Convert attach to flat-return style

Deduplicate the no-buffer and the import-fail case, and try to fall
through where we can. This will make it easier to shift the buffer
reference change later, so the attach subhandlers can reference the old
buffer when checking for compatibility.

Signed-off-by: Daniel Stone <daniels@collabora.com>

libweston/renderer-gl/gl-renderer.c

@@ -3044,20 +3044,8 @@ gl_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer)
 	weston_buffer_release_reference(&gs->buffer_release_ref,
 					es->buffer_release_ref.buffer_release);
 
-	if (!buffer) {
-		for (i = 0; i < gb->num_images; i++) {
-			egl_image_unref(gb->images[i]);
-			gb->images[i] = NULL;
-		}
-		gb->num_images = 0;
-		glDeleteTextures(gs->num_textures, gs->textures);
-		gs->num_textures = 0;
-		gb->buffer_type = BUFFER_TYPE_NULL;
-		gb->y_inverted = true;
-		gb->direct_display = false;
-		es->is_opaque = false;
-		return;
-	}
+	if (!buffer)
+		goto out;
 
 	switch (buffer->type) {
 	case WESTON_BUFFER_SHM:
@@ -3079,15 +3067,25 @@ gl_renderer_attach(struct weston_surface *es, struct weston_buffer *buffer)
 	if (ret)
 		return;
 
-	weston_log("unhandled buffer type!\n");
 	weston_buffer_reference(&gs->buffer_ref, NULL,
 				BUFFER_WILL_NOT_BE_ACCESSED);
 	weston_buffer_release_reference(&gs->buffer_release_ref, NULL);
+	weston_log("unhandled buffer type!\n");
+	weston_buffer_send_server_error(buffer,
+		"disconnecting due to unhandled buffer type");
+
+out:
+	for (i = 0; i < gb->num_images; i++) {
+		egl_image_unref(gb->images[i]);
+		gb->images[i] = NULL;
+	}
+	gb->num_images = 0;
+	glDeleteTextures(gs->num_textures, gs->textures);
+	gs->num_textures = 0;
 	gb->buffer_type = BUFFER_TYPE_NULL;
 	gb->y_inverted = true;
+	gb->direct_display = false;
 	es->is_opaque = false;
-	weston_buffer_send_server_error(buffer,
-		"disconnecting due to unhandled buffer type");
 }
 
 static void