libpcscspy: dump an output buffer only if the call succeeded

If the PC/SC call failed then the output buffer contains garbage and the
size could be wrong.

src/spy/libpcscspy.c

@@ -560,7 +560,12 @@ PCSC_API LONG SCardControl(SCARDHANDLE hCard,
  rv = spy.SCardControl(hCard, dwControlCode, pbSendBuffer, cbSendLength,
  pbRecvBuffer, cbRecvLength, lpBytesReturned);
  if (lpBytesReturned)
- spy_buffer(pbRecvBuffer, *lpBytesReturned);
+ {
+ if (SCARD_S_SUCCESS == rv)
+ spy_buffer(pbRecvBuffer, *lpBytesReturned);
+ else
+ spy_buffer(NULL, *lpBytesReturned);
+ }
  else
  spy_buffer(NULL, 0);
  Quit();
@@ -603,7 +608,12 @@ PCSC_API LONG SCardTransmit(SCARDHANDLE hCard,
  spy_long(-1);
  }
  if (pcbRecvLength)
- spy_buffer(pbRecvBuffer, *pcbRecvLength);
+ {
+ if (SCARD_S_SUCCESS == rv)
+ spy_buffer(pbRecvBuffer, *pcbRecvLength);
+ else
+ spy_buffer(NULL, *pcbRecvLength);
+ }
  else
  spy_buffer(NULL, 0);
  Quit();
@@ -697,16 +707,19 @@ PCSC_API LONG SCardGetAttrib(SCARDHANDLE hCard,
  if (NULL == pcbAttrLen)
  spy_buffer(NULL, 0);
  else
- {
- LPBYTE buffer;
-
- if (autoallocate)
- buffer = *(LPBYTE *)pbAttr;
+ if (rv != SCARD_S_SUCCESS)
+ spy_buffer(NULL, *pcbAttrLen);
  else
- buffer = pbAttr;
+ {
+ LPBYTE buffer;
 
- spy_buffer(buffer, *pcbAttrLen);
- }
+ if (autoallocate)
+ buffer = *(LPBYTE *)pbAttr;
+ else
+ buffer = pbAttr;
+
+ spy_buffer(buffer, *pcbAttrLen);
+ }
  Quit();
  return rv;
 }