fix: return at least one in sizeCalculation (#10832)

if post content is empty post cache should still consider its size to be at least one. fixes #10831

src/posts/cache.js

@@ -6,7 +6,7 @@ const meta = require('../meta');
 module.exports = cacheCreate({
 	name: 'post',
 	maxSize: meta.config.postCacheSize,
-	sizeCalculation: function (n) { return n.length; },
+	sizeCalculation: function (n) { return n.length || 1; },
 	ttl: 0,
 	enabled: global.env === 'production',
 });