Correctly handle received metadata

It did not work correctly, since it assumed that 'lt::torrent_plugin' is created at an earlier stage and is able to track all changes in the torrent state, but in reality it turned out that it was created after the torrent moved to the `downloading_metadata` state, so we had to additionally handle it in the constructor.

PR #16121.

src/base/bittorrent/nativetorrentextension.cpp

@@ -41,6 +41,7 @@ namespace
 NativeTorrentExtension::NativeTorrentExtension(const lt::torrent_handle &torrentHandle)
     : m_torrentHandle {torrentHandle}
 {
+    on_state(m_torrentHandle.status({}).state);
 }
 
 bool NativeTorrentExtension::on_pause()
@@ -56,7 +57,10 @@ bool NativeTorrentExtension::on_pause()
 void NativeTorrentExtension::on_state(const lt::torrent_status::state_t state)
 {
     if (m_state == lt::torrent_status::downloading_metadata)
-        m_torrentHandle.set_flags(lt::torrent_flags::stop_when_ready);
+    {
+        m_torrentHandle.unset_flags(lt::torrent_flags::auto_managed);
+        m_torrentHandle.pause();
+    }
 
     m_state = state;
 }