assetfilesource: Fix some leaks
assetfilesource: Fix some leaks

cfoch/ges,pitivi/gst-editing-services,cfoch/gst-editing-services,cfoch/gst-editing-services,cfoch/ges,cfoch/ges,pitivi/gst-editing-services,pitivi/gst-editing-services,pitivi/gst-editing-services,cfoch/gst-editing-services,cfoch/ges,cfoch/gst-editing-services