ytdl_hook: init fragment requires other fragments

With dash the first fragment was always considered an init fragment if
there wasn't a duration. However that only makes sense when there are
also other fragments, so check if there are other fragments in addition
to the lack of a duration.

player/lua/ytdl_hook.lua

@@ -297,7 +297,7 @@ local function edl_track_joined(fragments, protocol, is_live, base)
         local args = ""
 
         -- assume MP4 DASH initialization segment
-        if not fragments[1].duration then
+        if not fragments[1].duration and #fragments > 1 then
             msg.debug("Using init segment")
             args = args .. ",init=" .. edl_escape(join_url(base, fragments[1]))
             offset = 2