prompt: Fix restoring terminal pass down and use fd

fbshipit-source-id: bb28650

reader_posix.go

@@ -37,7 +37,7 @@ func (t *PosixReader) Open() error {
 
 // Close should be called after stopping input
 func (t *PosixReader) Close() error {
-	if err := term.Restore(); err != nil {
+	if err := term.RestoreFD(t.fd); err != nil {
 		_ = syscall.Close(t.fd)
 		return err
 	}

term/term.go

@@ -37,9 +37,14 @@ func getOriginalTermios(fd int) (*unix.Termios, error) {
 
 // Restore terminal's mode.
 func Restore() error {
-	o, err := getOriginalTermios(saveTermiosFD)
+	return RestoreFD(saveTermiosFD)
+}
+
+// RestoreFD restores terminal's mode for the given file descriptor.
+func RestoreFD(fd int) error {
+	o, err := getOriginalTermios(fd)
 	if err != nil {
 		return err
 	}
-	return termios.Tcsetattr(uintptr(saveTermiosFD), termios.TCSANOW, o)
+	return termios.Tcsetattr(uintptr(fd), termios.TCSANOW, o)
 }