[rygel] media-export: Prevent critical

[Jens Georg <jensgeorg src gnome org>]

commit ce5a57d11687d8a6bf9e0554cf66fcf230c56939
Author: Jens Georg <mail jensge org>
Date:   Sun Apr 10 17:08:39 2016 +0200

    media-export: Prevent critical
    
    Signed-off-by: Jens Georg <mail jensge org>

 .../rygel-media-export-root-container.vala         |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/src/plugins/media-export/rygel-media-export-root-container.vala 
b/src/plugins/media-export/rygel-media-export-root-container.vala
index 38b6980..362083b 100644
--- a/src/plugins/media-export/rygel-media-export-root-container.vala
+++ b/src/plugins/media-export/rygel-media-export-root-container.vala
@@ -528,7 +528,9 @@ public class Rygel.MediaExport.RootContainer : TrackableDbContainer {
         this.harvester.locations.remove_all (old_uris);
 
         if (!new_uris.is_empty) {
-            this.filesystem_container.disconnect (this.filesystem_signal_id);
+            if (this.filesystem_signal_id != 0) {
+                this.filesystem_container.disconnect (this.filesystem_signal_id);
+            }
             this.filesystem_signal_id = 0;
             this.harvester_signal_id = this.harvester.done.connect
                                             (on_initial_harvesting_done);