Fix links with invalid emoji in them.

InlinePatterns should return None on failure, not text that may
have placeholders in it.

(imported from commit f9d8d22b2b8cfa7a92ecf3e52a6c76b48e6f0175)

zerver/lib/bugdown/__init__.py

@@ -365,7 +365,7 @@ class Emoji(markdown.inlinepatterns.Pattern):
             src = 'static/third/gemoji/images/emoji/%s.png' % (name)
             return make_emoji(name, src, orig_syntax)
         else:
-            return orig_syntax
+            return None
 
 def fixup_link(link, target_blank=True):
     """Set certain attributes we want on every link."""

zerver/tests.py

@@ -3019,6 +3019,9 @@ int x = 3
                         "<p>%s</p>",
                         'http://technet.microsoft.com/en-us/library/Cc751099.rk20_25_big(l=en-us).mov'),
 
+         # Links that match other InlinePatterns
+         ('https://metacpan.org/module/Image::Resize::OpenCV', '<p>%s</p>', 'https://metacpan.org/module/Image::Resize::OpenCV'),
+
          # Just because it has a TLD and parentheses in it doesn't mean it's a link. Trac #1364
          ('a.commandstuff()', '<p>a.commandstuff()</p>', ''),
          ('love...it', '<p>love...it</p>', ''),