Some debug output.

print.c

@@ -94,6 +94,7 @@ cb_print_draw_page(GtkPrintOperation* UNUSED(print_operation), GtkPrintContext*
     return;
   }
 
+  girara_debug("printing page %d ...", page_number);
   render_lock(zathura->sync.render_thread);
   zathura_page_render(page, cairo, true);
   render_unlock(zathura->sync.render_thread);