[libxml2] xmllint --pretty crashed without following numeric argument

[Daniel Veillard <veillard src gnome org>]

commit 2205ff4b0d4a70ed986f28b27c4a2037f6f0af1f
Author: Tim Galeckas <tim galeckas com>
Date:   Thu Aug 29 16:44:33 2013 +0800

    xmllint --pretty crashed without following numeric argument
    
    https://bugzilla.gnome.org/show_bug.cgi?id=674789
    
    We need to check for NULL argument before calling atoi()

 xmllint.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)
---
diff --git a/xmllint.c b/xmllint.c
index 92e6b03..d69722c 100644
--- a/xmllint.c
+++ b/xmllint.c
@@ -3388,11 +3388,13 @@ main(int argc, char **argv) {
                 (!strcmp(argv[i], "--pretty"))) {
             i++;
 #ifdef LIBXML_OUTPUT_ENABLED
-            format = atoi(argv[i]);
-            if (format == 1) {
-                noblanks++;
-                xmlKeepBlanksDefault(0);
-            }
+       if (argv[i] != NULL) {
+                format = atoi(argv[i]);
+                if (format == 1) {
+                    noblanks++;
+                    xmlKeepBlanksDefault(0);
+                }
+       }
 #endif /* LIBXML_OUTPUT_ENABLED */
        }
 #ifdef LIBXML_READER_ENABLED