Exactly one link in a paragraph with a bookmark causes failure to render page

[isaacwhite]

Context (Environment)

Within a particular paragraph, if there are exactly two links and one is a bookmark (not a normal link), the table of contents logic within Library can crash.

Expected Behavior

When a paragraph does not match expectations for table of contents, the link replacement should be ignored and left as-is.

To Reproduce

Within a single paragraph, add a bookmark. Then add a normal link later in the paragraph. Reload the library page and observe the following trace:

TypeError: Cannot read property \'match\' of undefined
  at checkForTableOfContents (/usr/src/app/server/formatter.js:156:25)
  at Node.$p.each (/usr/src/app/server/formatter.js:26:31)
  at initialize.exports.each (/usr/src/app/node_modules/cheerio/lib/api/traversing.js:300:24)
  at normalizeHtml (/usr/src/app/server/formatter.js:22:6)
  at getProcessedHtml (/usr/src/app/server/formatter.js:231:14)
  at Object.exports.getProcessedDocAttributes (/usr/src/app/server/formatter.js:243:25)
  at exports.fetchDoc 

Possible Solution

The table of contents logic should be made more robust, so that link tags without href attributes are ignored.