[grilo-plugins] metrolyrics: Do not crash when parser fails

[Victor Toso de Carvalho <victortoso src gnome org>]

commit a692b9e81fcab25b8d417328d5fc7bea9da12bbf
Author: Victor Toso <me victortoso com>
Date:   Sat Aug 29 11:51:15 2015 +0200

    metrolyrics: Do not crash when parser fails
    
    (lt-grilo-test-ui-0.2:8463): Grilo-WARNING **: [lua-library]
    grl-lua-library.c:509: calling source callback function fail
    (fetch_page_cb) grl-metrolyrics.lua:99:
    attempt to index a nil value (local 'feed')'
    
    https://bugzilla.gnome.org/show_bug.cgi?id=754275

 src/lua-factory/sources/grl-metrolyrics.lua |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)
---
diff --git a/src/lua-factory/sources/grl-metrolyrics.lua b/src/lua-factory/sources/grl-metrolyrics.lua
index 02670d8..cb42f5d 100644
--- a/src/lua-factory/sources/grl-metrolyrics.lua
+++ b/src/lua-factory/sources/grl-metrolyrics.lua
@@ -96,6 +96,11 @@ function metrolyrics_get_lyrics(feed)
 
   -- remove html noise
   feed = feed:match(lyrics_body)
+  if not feed then
+    grl.warning ("This Lyrics do not match our parser! Please file a bug!")
+    return nil
+  end
+
   for _, it in ipairs (noise_array) do
     feed = feed:gsub(it.noise, it.sub)
   end