sed: open input files sequentially to avoid EMFILE

Currently, sed pre-opens all files, which may cause EMFILE errors
on systems with low ulimit -n.  Change sed to open one file at a time.

function                                             old     new   delta
get_next_line                                        177     235     +58
sed_main                                             682     652     -30
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/1 up/down: 58/-30)             Total: 28 bytes

Based on the patch by Daniel Borca <dborca@yahoo.com>

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/libbb/fclose_nonstdin.c b/libbb/fclose_nonstdin.c
index 5ce9d5b..1b14413 100644
--- a/libbb/fclose_nonstdin.c
+++ b/libbb/fclose_nonstdin.c
@@ -18,7 +18,8 @@
 {
 	/* Some more paranoid applets want ferror() check too */
 	int r = ferror(f); /* NB: does NOT set errno! */
-	if (r) errno = EIO; /* so we'll help it */
+	if (r)
+		errno = EIO; /* so we'll help it */
 	if (f != stdin)
 		return (r | fclose(f)); /* fclose does set errno on error */
 	return r;