Move render_to_body logic to return a spaced string to AC::Rendering

This seems to be required only when calling render :partial with an
empty collection from a controller. This call happens to return no
content, letting the response body empty, which means to Rails that it
should go on and try to find a template to render based on the current
action name, thus failing hard.

Although tests keep all green, we need to check a better way to fix
this.

actionpack/lib/action_controller/metal/compatibility.rb

@@ -13,9 +13,5 @@ class << self
         :@_view_runtime, :@_stream, :@_url_options, :@_action_has_layout
       ]
     end
-
-    def render_to_body(options)
-      super || " "
-    end
   end
 end

actionpack/lib/action_controller/metal/rendering.rb

@@ -29,6 +29,10 @@ def render_to_string(*)
       self.response_body = nil
     end
 
+    def render_to_body(*)
+      super || " "
+    end
+
     private
 
     # Normalize arguments by catching blocks and setting them on :update.

actionpack/lib/action_controller/metal/streaming.rb

@@ -216,7 +216,7 @@ def _process_options(options) #:nodoc:
       end
     end
 
-    # Call render_to_body if we are streaming instead of usual +render+.
+    # Call render_body if we are streaming instead of usual +render+.
     def _render_template(options) #:nodoc:
       if options.delete(:stream)
         Rack::Chunked::Body.new view_renderer.render_body(view_context, options)

actionpack/lib/action_view/test_case.rb

@@ -233,10 +233,8 @@ def method_missing(selector, *args)
           super
         end
       end
-
     end
 
     include Behavior
-
   end
 end

actionpack/test/controller/filters_test.rb

@@ -815,8 +815,6 @@ def test_process(controller, action = "show")
     end
 end
 
-
-
 class PostsController < ActionController::Base
   module AroundExceptions
     class Error < StandardError ; end