Fix slide might not provide slideOptions meta

Author: jackycute

lib/response.js

@@ -575,7 +575,7 @@ function showPublishSlide (req, res, next) {
         updatetime: updatetime,
         url: origin,
         body: markdown,
-        theme: utils.isRevealTheme(meta.slideOptions.theme),
+        theme: meta.slideOptions && utils.isRevealTheme(meta.slideOptions.theme),
         meta: JSON.stringify(extracted.meta),
         useCDN: config.usecdn,
         owner: note.owner ? note.owner.id : null,