dup.2: ffix

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/dup.2

@@ -247,6 +247,7 @@ before calling
 because of the race condition described above.
 Instead, code something like the following could be used:
 .PP
+.in +4n
 .EX
 /* Obtain a duplicate of 'newfd' that can subsequently
    be used to check for close() errors; an EBADF error
@@ -272,6 +273,7 @@ Instead, code something like the following could be used:
     }
 }
 .EE
+.in
 .SH SEE ALSO
 .BR close (2),
 .BR fcntl (2),