[gnome-software] trivial: Fix a crash if the steam download is corrupt

[Richard Hughes <rhughes src gnome org>]

commit 3a857300e12c28289bd79f4e57d958aaa39e84b1
Author: Richard Hughes <richard hughsie com>
Date:   Tue Apr 12 11:37:30 2016 +0100

    trivial: Fix a crash if the steam download is corrupt

 src/plugins/gs-plugin-steam.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/plugins/gs-plugin-steam.c b/src/plugins/gs-plugin-steam.c
index a63eb55..faedb03 100644
--- a/src/plugins/gs-plugin-steam.c
+++ b/src/plugins/gs-plugin-steam.c
@@ -332,6 +332,10 @@ gs_plugin_steam_capture (const gchar *html,
        guint start_len;
        guint end_len;
 
+       /* invalid */
+       if (html == NULL)
+               return NULL;
+
        /* find @start */
        start_len = strlen (start);
        for (i = *offset; html[i] != '\0'; i++) {