Ruby

win32.c: fix function pointer

• win32/win32.c (rb_w32_set_thread_description): fix the condition
  if the API function pointer is found.
  [ruby-core:82494] [Bug #13845]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59678 b2dd03c8-39d4-4d8f-98ff-823fe69b080e