[gnome-control-center] hostname-helper: don't read past '\0'

[Bastien Nocera <hadess src gnome org>]

commit d153b9b4eec6bb199b6a5bceba09e853579f195c
Author: Mohammed Sadiq <sadiq sadiqpk org>
Date:   Fri May 5 17:40:33 2017 +0530

    hostname-helper: don't read past '\0'
    
    g_utf8_find_next_char() doesn't do checks whether the char
    is '\0' or not. We have to take care of that ourself.
    
    This commit fixes heap-buffer-overflow found by test-hostname
    
    ERROR: AddressSanitizer: heap-buffer-overflow on address
    READ of size 1 at 0x60200000cd76 thread T0
     #0 0x7f8b26920d08 in g_utf8_find_next_char glib/glib/gutf8.c:179
     #1 0x55c2b8eacaee in pretty_hostname_to_ssid gnome-control-center/shell/hostname-helper.c:199
    
    https://bugzilla.gnome.org/show_bug.cgi?id=782216

 shell/hostname-helper.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/shell/hostname-helper.c b/shell/hostname-helper.c
index b09d93f..df59697 100644
--- a/shell/hostname-helper.c
+++ b/shell/hostname-helper.c
@@ -208,6 +208,9 @@ pretty_hostname_to_ssid (const char *pretty)
                        break;
                }
 
+               if (*p == '\0')
+                       break;
+
                prev = p;
        }