fixes for transfer resume

Fix resuming of downloads, which do not have a transfer info file to read.

When checking upload progress, use the MVar, rather than re-reading
the info file.

Catch exceptions in the transfer action. Required a tryAnnex.

Command/TransferInfo.hs

@@ -47,7 +47,7 @@ start (k:[]) = do
 				, transferKey = key
 				}
 			info <- liftIO $ startTransferInfo file
-			(update, tfile) <- mkProgressUpdater t info
+			(update, tfile, _) <- mkProgressUpdater t info
 			liftIO $ mapM_ void
 				[ tryIO $ forever $ do
 					bytes <- readish <$> getLine