* load.c (load_lock): fix not to delete thread shield twice.
  it may break the shield locked by another thread.
  [Bug #7530] [ruby-core:50645]

* test/ruby/test_require.rb: a test for above.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38744 b2dd03c8-39d4-4d8f-98ff-823fe69b080e