curl: 41: `main_checkfds()` pipe reuse leaks proxy credentials into HTTPS upload body

Summary When curl is launched with stdin fd 0 and stderr fd 2 closed, maincheckfds in src/toolmain.c can assign opposite ends of the same pipe to fd 0 and fd 2. In verbose mode with a stdin-based upload through an authenticated proxy, the Proxy-Authorization header written to stderr becomes...