src/file_io.c : Prevent potential divide-by-zero.

Closes: https://github.com/erikd/libsndfile/issues/92

Upstream-Status: Backport

Fixes CVE-2014-9756

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
Signed-off-by: Maxin B. John <maxin.john@intel.com>
---
diff -Naur libsndfile-1.0.25-orig/src/file_io.c libsndfile-1.0.25/src/file_io.c
--- libsndfile-1.0.25-orig/src/file_io.c	2011-01-19 12:12:28.000000000 +0200
+++ libsndfile-1.0.25/src/file_io.c	2015-11-04 15:02:04.337395618 +0200
@@ -358,6 +358,9 @@
 {	sf_count_t total = 0 ;
 	ssize_t	count ;
 
+    if (bytes == 0 || items == 0)
+        return 0 ;
+
 	if (psf->virtual_io)
 		return psf->vio.write (ptr, bytes*items, psf->vio_user_data) / bytes ;