screenshot: Use correct buffer size for transformed outputs.

This is a workaround for screenshots with transformed outputs. It reorders
the output positions so the correct buffer size is determined for the final
image. This assumes the outputs are in succession on the x axis. The outputs
are rendered in their transformed state.

clients/screenshot.c

@@ -205,6 +205,12 @@ set_buffer_size(int *width, int *height)
 	struct screenshooter_output *output;
 	min_x = min_y = INT_MAX;
 	max_x = max_y = INT_MIN;
+	int position = 0;
+
+	wl_list_for_each_reverse(output, &output_list, link) {
+		output->offset_x = position;
+		position += output->width;
+	}
 
 	wl_list_for_each(output, &output_list, link) {
 		min_x = MIN(min_x, output->offset_x);