[grilo-plugins/wip/hadess/fix-atom-podcasts-crash] podcasts: Fix crash trying to parse unsupported format

[Bastien Nocera <hadess src gnome org>]

commit 96fbf81e1227aa5190ea800005deeea1e647bf4b
Author: Bastien Nocera <hadess hadess net>
Date:   Mon Feb 11 22:11:21 2019 +0100

    podcasts: Fix crash trying to parse unsupported format
    
    1. Add an Atom feed to the Podcasts plugin
    2. Try to browse that Atom feed
    3. RSS parser crashes as it doesn't know how to parse Atom
    
    ==8560== Invalid read of size 8
    ==8560==    at 0x1BBD36DF: parse_feed (grl-podcasts.c:1274)
    ==8560==    by 0x1BBD36DF: read_feed_cb (grl-podcasts.c:1365)
    ==8560==    by 0x1BBD1272: read_done_cb (grl-podcasts.c:494)
    ==8560==    by 0x52F1A69: g_simple_async_result_complete (in /usr/lib64/libgio-2.0.so.0.5800.3)
    ==8560==    by 0x1BB48D2F: read_async_cb (grl-net-wc.c:619)
    ==8560==  Address 0x10 is not stack'd, malloc'd or (recently) free'd

 src/podcasts/grl-podcasts.c | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/src/podcasts/grl-podcasts.c b/src/podcasts/grl-podcasts.c
index a9e045e..6c91e80 100644
--- a/src/podcasts/grl-podcasts.c
+++ b/src/podcasts/grl-podcasts.c
@@ -1269,6 +1269,13 @@ parse_feed (OperationSpec *os, const gchar *str, GError **error)
   xmlXPathFreeObject (xpathObj);
   xpathObj = NULL;
 
+  if(podcast_data == NULL) {
+    *error = g_error_new_literal (GRL_CORE_ERROR,
+                                  os->error_code,
+                                  _("Failed to parse podcast contents"));
+    goto free_resources;
+  }
+
   /* Check podcast pubDate (if available), if it has not been updated
      recently then we can use the cache and avoid parsing the feed */
   if (podcast_data->published != NULL) {