Scrub only after converting strings to UTF-8

Scrubbing an ASCII-8BIT string isn't ever going to remove anything, because
there's no code point that isn't valid 8-bit ASCII.  Since we'd really
prefer it if everything were UTF-8 anyway, we'll just assume, for now, that
whatever comes out of SimpleRSS is probably UTF-8, and just nuke anything
that isn't a valid UTF-8 codepoint.

Of course, the *real* bug here is that SimpleRSS [unilaterally converts
everything to
ASCII-8BIT](cardmagic/simple-rss#15).  It's
presumably *far* too much to ask that it detects the encoding of the source
RSS feed and marks the parsed strings with the correct encoding...

app/jobs/scheduled/poll_feed.rb

@@ -86,11 +86,11 @@ def url
       end
 
       def content
-        @article_rss_item.content.try(:scrub) || @article_rss_item.description.try(:scrub)
+        @article_rss_item.content.try(:force_encoding, "UTF-8").try(:scrub) || @article_rss_item.description.try(:force_encoding, "UTF-8").try(:scrub)
       end
 
       def title
-        @article_rss_item.title.scrub
+        @article_rss_item.title.force_encoding("UTF-8").scrub
       end
 
       def user