TypeError in update_links()

Created by: grawlinson

Well, this is definitely a weird one...

When updating the arch-wiki-docs package to the latest commit (b6c20fd from 216a217), I'm getting a TypeError that throws this:

==> Starting prepare()...
Downloading CSS...
  ArchWikiOffline.css
Available namespaces:
  -2 -- Media
  -1 -- Special
   0 -- Main
   1 -- Talk
   2 -- User
   3 -- User talk
   4 -- ArchWiki
   5 -- ArchWiki talk
   6 -- File
   7 -- File talk
   8 -- MediaWiki
   9 -- MediaWiki talk
  10 -- Template
  11 -- Template talk
  12 -- Help
  13 -- Help talk
  14 -- Category
  15 -- Category talk
  3000 -- DeveloperWiki
  3001 -- DeveloperWiki talk
Processing namespace 0...
  [skipping] .NET
  [downloading] .NET Core (Español)
Traceback (most recent call last):
  File "/build/arch-wiki-docs/src/arch-wiki-docs/arch-wiki-docs.py", line 41, in <module>
    downloader.process_namespace(ns)
  File "/build/arch-wiki-docs/src/arch-wiki-docs/ArchWiki/downloader.py", line 96, in process_namespace
    text = self.optimizer.optimize(fname, r.text)
  File "/build/arch-wiki-docs/src/arch-wiki-docs/ArchWiki/optimizer.py", line 31, in optimize
    self.update_links(root, relbase)
  File "/build/arch-wiki-docs/src/arch-wiki-docs/ArchWiki/optimizer.py", line 102, in update_links
    href += "#" + fragment
TypeError: unsupported operand type(s) for +=: 'NoneType' and 'str'

https://github.com/lahwaacz/arch-wiki-docs/blob/b6c20fdf329187a30f9e1367167601f9a887178d/ArchWiki/optimizer.py#L80-L109

This is a bit confusing because one of the first if statements in that particular function is checking if href is not None.