*: use NULL for null pointers

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

e2fsprogs/old_e2fsprogs/ext2fs/imager.c

@@ -333,7 +333,7 @@ errout:
  */
 errcode_t ext2fs_image_bitmap_read(ext2_filsys fs, int fd, int flags)
 {
-	char		*ptr, *buf = 0;
+	char		*ptr, *buf = NULL;
 	int		size;
 	ssize_t		actual;
 	errcode_t	retval;