bug in 1.5.1 ,cpu 100% and Paging auto jump

[Origin-zhao]

1. when i open a new page of topic list,it's take too long time and server's cpu 100%
   

2. when i click next page but paging auto jump back
   

3. my server config

• cpu 1 core
  RAM 1G
  SSD 25G
  docker(debian 9) mogonDB v3.4.4

4. I use performance monitoring tools，found something.
   the pge of sitemap/topics.(\d+).xml take too long time

[Origin-zhao]

CPU very hight, just open page, nothing to do

[Giggiux]

This post is deleted!

[baris]

I noticed the jumping on pagination as well, will work on a fix for this.

[baris]

https://github.com/NodeBB/NodeBB/issues/5752