[gatsby-source-wordpress] Do not assume entities will exist (#5004)
[gatsby-source-wordpress] Do not assume entities will exist (#5004)

* Update normalize.js

* check if we have entities of tags/categories/users before trying to link to them

mingaldrichgan/gatsby,fk/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,ChristopherBiscardi/gatsby,gatsbyjs/gatsby,fk/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,mingaldrichgan/gatsby,ChristopherBiscardi/gatsby,0x80/gatsby,fk/gatsby,0x80/gatsby,gatsbyjs/gatsby,gatsbyjs/gatsby,0x80/gatsby,ChristopherBiscardi/gatsby,ChristopherBiscardi/gatsby