Show real LoadError on helpers require

When helper try to require missing file rails will throw exception about
missing helper.

  # app/helpers/my_helper.rb

  require 'missing'

  module MyHelper
  end

And when we try do load helper

  class ApplicationController
    helper :my
  end

Rails will throw exception. This is wrong because there is a helper
file.

  Missing helper file helpers/my_helper.rb

Now when helper try to require non-existed file rails will throw proper
exception.

  No such file to load -- missing

1 files changed, 7 insertions, 0 deletions

diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index ea1d090bc2..3105dbcc42 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Fix an issue where rails raise exception about missing helper where it
+    should throw `LoadError`. When helper file exists and only loaded file from
+    this helper does not exist rails should throw LoadError instead of
+    `MissingHelperError`.
+
+    *Piotr Niełacny*
+
 *   Fix `ActionDispatch::ParamsParser#parse_formatted_parameters` to rewind body input stream on
     parsing json params.