CloseHandle docs says that the return is non-zero, does not say TRUE(1)

Summary:
say it is TRUE(1). Add assert.
Closes https://github.com/facebook/rocksdb/pull/3630

Differential Revision: D7346895

Pulled By: ajkr

fbshipit-source-id: a46075aa4dd89f32520230606adecccecc874cdf

port/win/win_thread.cc

@@ -138,7 +138,9 @@ void WindowsThread::join() {
       "WaitForSingleObjectFailed: thread join");
   }
 
-  CloseHandle(reinterpret_cast<HANDLE>(data_->handle_));
+  BOOL rc;
+  rc = CloseHandle(reinterpret_cast<HANDLE>(data_->handle_));
+  assert(rc != 0);
   data_->handle_ = 0;
 }
 
@@ -154,7 +156,7 @@ bool WindowsThread::detach() {
   BOOL ret = CloseHandle(reinterpret_cast<HANDLE>(data_->handle_));
   data_->handle_ = 0;
 
-  return (ret == TRUE);
+  return (ret != 0);
 }
 
 void  WindowsThread::swap(WindowsThread& o) {