Improve SCardDisconnect fix

Same justification as for the previous patch. RFReaderInfoById() may
return SCARD_E_READER_UNAVAILABLE.

src/winscard.c

@@ -841,7 +841,7 @@ LONG SCardDisconnect(SCARDHANDLE hCard, DWORD dwDisposition)
 	/* get rContext corresponding to hCard */
 	rv = RFReaderInfoById(hCard, &rContext);
 	/* ignore reader removal */
-	if (SCARD_E_INVALID_VALUE == rv)
+	if (SCARD_E_INVALID_VALUE == rv || SCARD_E_READER_UNAVAILABLE == rv)
 		return SCARD_S_SUCCESS;
 	if (rv != SCARD_S_SUCCESS)
 		return rv;