bugfix: wayback machine missing content-location

It seems the wayback machine sometimes fails to return a Content-Location header altogether. It is unclear why or how it happens, but it did here on my personal setup: Subject: Cron <anarcat@marcos> nice feed2exec --syslog INFO fetch To: anarcat@anarc.at Date: Sat, 27 Jan 2018 12:06:34 -0500 anarcat just posted: A summary of my 2017 work https://t.co/FjMMvBpLG7 Toot posted: [32mhttps://social.weho.st/@anarcat/99422857762709389[0m plugin generated exception: 'content-location', skipping Traceback (most recent call last): File "/usr/local/lib/python3.5/dist-packages/feed2exec/plugins/__init__.py", line 105, in output return plugin.output(*args, feed=feed, item=item, lock=lock) File "/usr/local/lib/python3.5/dist-packages/feed2exec/plugins/wayback.py", line 34, in output location = res.headers['Content-Location'] File "/usr/lib/python3/dist-packages/requests/structures.py", line 54, in __getitem__ return self._store[key.lower()][1] KeyError: 'content-location' plugin generated exception: 'content-location', skipping Traceback (most recent call last): File "/usr/local/lib/python3.5/dist-packages/feed2exec/plugins/__init__.py", line 105, in output return plugin.output(*args, feed=feed, item=item, lock=lock) File "/usr/local/lib/python3.5/dist-packages/feed2exec/plugins/wayback.py", line 34, in output location = res.headers['Content-Location'] File "/usr/lib/python3/dist-packages/requests/structures.py", line 54, in __getitem__ return self._store[key.lower()][1] KeyError: 'content-location' It is unclear why this happens or how to reproduce, so I don't have a unit test for this just yet. But we should guard against bad data anyways, so handling missing headers is a good idea anyways.