Fix appname resolution when outside Rails context

The adapter can be used outside a Rails context so TinyTDS appname config should
be able to be resolved if a Rails application was not detected.

Fix #942.

Author: wpolicarpo

lib/active_record/connection_adapters/sqlserver_adapter.rb

@@ -119,9 +119,9 @@ def config_appname(config)
         end
 
         def rails_application_name
-          return nil if Rails.application.nil?
-
           Rails.application.class.name.split("::").first
+        rescue
+          nil # Might be in a Rails context so we fallback to `nil`.
         end
 
         def config_login_timeout(config)