curl: CURLX_SET_BINMODE(NULL) can call fileno(NULL) and cause undefined behavior / crash

Summary ------- Calling the CURLXSETBINMODEstream macro with stream == NULL leads to an unguarded call to filenoNULL in toolbinmode.h, which is undefined behavior and may crash the process. This is a robustness/UB issue and should be corrected by guarding against NULL streams before calling filen...