[gupnp-dlna] Exit early if no extractor can be found

[Jens Georg <jensgeorg src gnome org>]

commit cd67b9b2c771623fae793675beacdfe721b11d7a
Author: Jens Georg <mail jensge org>
Date:   Wed Jul 1 00:22:06 2015 +0200

    Exit early if no extractor can be found
    
    Signed-off-by: Jens Georg <mail jensge org>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=751634

 libgupnp-dlna/gupnp-dlna-profile-guesser.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/libgupnp-dlna/gupnp-dlna-profile-guesser.c b/libgupnp-dlna/gupnp-dlna-profile-guesser.c
index ef9ce94..11fa355 100644
--- a/libgupnp-dlna/gupnp-dlna-profile-guesser.c
+++ b/libgupnp-dlna/gupnp-dlna-profile-guesser.c
@@ -295,6 +295,8 @@ gupnp_dlna_profile_guesser_guess_profile_async
         g_return_val_if_fail (error == NULL || *error == NULL, FALSE);
 
         extractor = gupnp_dlna_metadata_backend_get_extractor ();
+        g_return_val_if_fail (extractor != NULL, FALSE);
+
         extractor_error = NULL;
         id = g_signal_connect_swapped (extractor,
                                        "done",
@@ -348,6 +350,8 @@ gupnp_dlna_profile_guesser_guess_profile_sync
 
         extraction_error = NULL;
         extractor = gupnp_dlna_metadata_backend_get_extractor ();
+        g_return_val_if_fail (extractor != NULL, NULL);
+
         info = gupnp_dlna_metadata_extractor_extract_sync (extractor,
                                                            uri,
                                                            timeout_in_ms,