Avoid data corruption when rechecking paused torrents

Libtorrent can recheck only unpaused torrents. We get around this by
unpausing the torrent, issuing the recheck and pausing again after we
get alerted by libtorrent that the recheck has finished. This alert is
asyncronous. There is a small time frame where the program might start
downloading and writing data to the file before we pause it. This can
lead to data corruption if the file on disk is totally different that
the one expected by the torrent AND the file on disk is a valid file on
its own. OR in case the user points the new torrent to the wrong
directory by mistake.
To get around this the torrent is placed in upload_mode and out of
automanagement.

src/base/bittorrent/torrenthandle.cpp

@@ -1277,7 +1277,7 @@ void TorrentHandle::forceRecheck()
 
     if (isPaused()) {
         m_pauseAfterRecheck = true;
-        resume();
+        resume_impl(true, true);
     }
 
     m_nativeHandle.force_recheck();
@@ -1345,12 +1345,17 @@ void TorrentHandle::pause()
 }
 
 void TorrentHandle::resume(bool forced)
+{
+    resume_impl(forced, false);
+}
+
+void TorrentHandle::resume_impl(bool forced, bool uploadMode)
 {
     if (hasError())
         m_nativeHandle.clear_error();
     m_hasMissingFiles = false;
-    m_nativeHandle.set_upload_mode(false);
     m_nativeHandle.auto_managed(!forced);
+    m_nativeHandle.set_upload_mode(uploadMode);
     m_nativeHandle.resume();
 }
 

src/base/bittorrent/torrenthandle.h

@@ -406,6 +406,7 @@ namespace BitTorrent
         void handleMetadataReceivedAlert(libtorrent::metadata_received_alert *p);
         void handleStatsAlert(libtorrent::stats_alert *p);
 
+        void resume_impl(bool forced, bool uploadMode);
         bool isMoveInProgress() const;
         QString nativeActualSavePath() const;