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.

lib/discourse.rb

@@ -128,7 +128,11 @@ module Discourse
     if Rails.env.development?
       plugin_hash = Digest::SHA1.hexdigest(all_plugins.map { |p| p.path }.sort.join('|'))
       hash_file = "#{Rails.root}/tmp/plugin-hash"
-      old_hash = File.read(hash_file) rescue nil
+
+      old_hash = begin
+        File.read(hash_file)
+      rescue Errno::ENOENT
+      end
 
       if old_hash && old_hash != plugin_hash
         puts "WARNING: It looks like your discourse plugins have recently changed."
@@ -236,7 +240,13 @@ module Discourse
   end
 
   def self.route_for(uri)
-    uri = URI(uri) rescue nil unless uri.is_a?(URI)
+    unless uri.is_a?(URI)
+      uri = begin
+        URI(uri)
+      rescue URI::InvalidURIError
+      end
+    end
+
     return unless uri
 
     path = uri.path || ""