[dash] Show fragment count with --live-from-start (#3493)

Authored by: flashdagger

yt_dlp/downloader/fragment.py

@@ -242,6 +242,9 @@ class FragmentFD(FileDownloader):
             if s['status'] not in ('downloading', 'finished'):
                 return
 
+            if not total_frags and ctx.get('fragment_count'):
+                state['fragment_count'] = ctx['fragment_count']
+
             if ctx_id is not None and s.get('ctx_id') != ctx_id:
                 return
 
@@ -450,6 +453,7 @@ class FragmentFD(FileDownloader):
             fatal, count = is_fatal(fragment.get('index') or (frag_index - 1)), 0
             while count <= fragment_retries:
                 try:
+                    ctx['fragment_count'] = fragment.get('fragment_count')
                     if self._download_fragment(ctx, fragment['url'], info_dict, headers):
                         break
                     return