Remove use of rescue nil.

* `rescue nil` is a really bad pattern to use in our code base.
  We should rescue errors that we expect the code to throw and
  not rescue everything because we're unsure of what errors the
  code would throw. This would reduce the amount of pain we face
  when debugging why something isn't working as expexted. I've
  been bitten countless of times by errors being swallowed as a
  result during debugging sessions.

app/models/topic_link_click.rb

@@ -16,7 +16,10 @@ class TopicLinkClick < ActiveRecord::Base
     url = args[:url][0...TopicLink.max_url_length]
     return nil if url.blank?
 
-    uri = URI.parse(url) rescue nil
+    uri = begin
+      URI.parse(url)
+    rescue URI::InvalidURIError
+    end
 
     urls = Set.new
     urls << url
@@ -43,7 +46,11 @@ class TopicLinkClick < ActiveRecord::Base
     # add a cdn link
     if uri
       if Discourse.asset_host.present?
-        cdn_uri = URI.parse(Discourse.asset_host) rescue nil
+        cdn_uri = begin
+          URI.parse(Discourse.asset_host)
+        rescue URI::InvalidURIError
+        end
+
         if cdn_uri && cdn_uri.hostname == uri.hostname && uri.path.starts_with?(cdn_uri.path)
           is_cdn_link = true
           urls << uri.path[cdn_uri.path.length..-1]
@@ -51,7 +58,11 @@ class TopicLinkClick < ActiveRecord::Base
       end
 
       if SiteSetting.Upload.s3_cdn_url.present?
-        cdn_uri = URI.parse(SiteSetting.Upload.s3_cdn_url) rescue nil
+        cdn_uri = begin
+          URI.parse(SiteSetting.Upload.s3_cdn_url)
+        rescue URI::InvalidURIError
+        end
+
         if cdn_uri && cdn_uri.hostname == uri.hostname && uri.path.starts_with?(cdn_uri.path)
           is_cdn_link = true
           path = uri.path[cdn_uri.path.length..-1]