qemu-nbd: Close inherited stderr

Close inherited stderr of the parent if fork_process is false.
Otherwise no one will close it. (introduced by e6df58a5)

This only affected 'qemu-nbd -c /dev/nbd0'.
Signed-off-by: NRaphael Pour <raphael.pour@hetzner.com>
Message-Id: <d8ddc993-9816-836e-a3de-c6edab9d9c49@hetzner.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
[eblake: Enhance commit message]
Signed-off-by: NEric Blake <eblake@redhat.com>
(cherry picked from commit 0eaf453e)
Signed-off-by: NMichael Roth <mdroth@linux.vnet.ibm.com>

qemu-nbd.c

@@ -1022,7 +1022,11 @@ int main(int argc, char **argv)
         } else if (pid == 0) {
             close(stderr_fd[0]);
 
-            old_stderr = dup(STDERR_FILENO);
+            /* Remember parent's stderr if we will be restoring it. */
+            if (fork_process) {
+                old_stderr = dup(STDERR_FILENO);
+            }
+
             ret = qemu_daemon(1, 0);
 
             /* Temporarily redirect stderr to the parent's pipe...  */