Use cairo_status_to_string for descriptive errors.

i3lock.c

@@ -657,8 +657,8 @@ int main(int argc, char *argv[]) {
         img = cairo_image_surface_create_from_png(image_path);
         /* In case loading failed, we just pretend no -i was specified. */
         if (cairo_surface_status(img) != CAIRO_STATUS_SUCCESS) {
-            fprintf(stderr, "Could not load image \"%s\": cairo surface status %d\n",
-                    image_path, cairo_surface_status(img));
+            fprintf(stderr, "Could not load image \"%s\": %s\n",
+                    image_path, cairo_status_to_string(cairo_surface_status(img)));
             img = NULL;
         }
     }