8430 dir_is_empty_readdir() doesn't properly handle error from fdopendir()

illumos/illumos-gate@ba6e7e6505
ba6e7e6505

https://www.illumos.org/issues/8430
  we should close dirfd if fdopendir() fails.

Reviewed by: Serapheim Dimitropoulos <serapheim@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Yuri Pankov <yuri.pankov@nexenta.com>
Reviewed by: Igor Kozhukhov <igor@dilos.org>
Approved by: Robert Mustacchi <rm@joyent.com>
Author: Sowrabha Gopal <sowrabha.gopal@delphix.com>

lib/libzfs/common/libzfs_mount.c

@@ -209,6 +209,7 @@ dir_is_empty_readdir(const char *dirname)
 	}
 
 	if ((dirp = fdopendir(dirfd)) == NULL) {
+		(void) close(dirfd);
 		return (B_TRUE);
 	}