Fixed output_buffer encoding problem [#5179]

Signed-off-by: NSantiago Pastorino <santiago@wyeworks.com>
Signed-off-by: NJosé Valim <jose.valim@gmail.com>

actionpack/lib/action_view/helpers/capture_helper.rb

@@ -165,7 +165,7 @@ def content_for?(name)
       def with_output_buffer(buf = nil) #:nodoc:
         unless buf
           buf = ActionView::OutputBuffer.new
-          buf.force_encoding(output_buffer.encoding) if output_buffer && buf.respond_to?(:force_encoding)
+          buf.force_encoding(output_buffer.encoding) if output_buffer.respond_to?(:encoding) && buf.respond_to?(:force_encoding)
         end
         self.output_buffer, old_buffer = buf, output_buffer
         yield

actionpack/test/template/javascript_helper_test.rb

@@ -89,6 +89,15 @@ def test_link_to_function_with_href
       link_to_function("Greeting", "alert('Hello world!')", :href => 'http://example.com/')
   end
 
+  def test_link_to_function_with_inner_block
+    html = link_to_function("Greet me!") do |page|
+      content_tag :h1 do
+        'Hi'
+      end
+    end
+  end
+
+
   def test_javascript_tag
     self.output_buffer = 'foo'