internal: Add a macro to make it easier to get the end of a TimelineElement
internal: Add a macro to make it easier to get the end of a TimelineElement

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