use existing fail_fd descriptor value FAIL_FD

alib2std/src/extensions/fdstream.cpp

@@ -83,7 +83,7 @@ fdaccessor::fdaccessor ( int new_fd, int fallback_fd ) {
 		fd = fallback_fd;
 		redirected = false;
 	} else {
-		fd = -1;
+		fd = FAIL_FD;
 		redirected = false;
 	}
 }
@@ -99,7 +99,7 @@ bool fdaccessor::is_redirected ( ) const {
 ofdstream::ofdstream ( int fd, int fallback_fd ) : fda ( fd, fallback_fd ), fdbuf ( fda.get_fd ( ) ) {
 	this->init ( & fdbuf );
-	if ( fda.get_fd ( ) == -1 )
+	if ( fda.get_fd ( ) == FAIL_FD )
 		setstate ( ios_base::failbit );
 }
@@ -113,7 +113,7 @@ bool ofdstream::is_redirected ( ) const {
 ifdstream::ifdstream ( int fd, int fallback_fd ) : fda ( fd, fallback_fd ), fdbuf ( fda.get_fd ( ) ) {
 	this->init ( & fdbuf );
-	if ( fda.get_fd ( ) == -1 )
+	if ( fda.get_fd ( ) == FAIL_FD )
 		setstate ( ios_base::failbit );
 }