addurl, importfeed: Fix failure when annex.securehashesonly is set

The temporary URL key used for the download, before the real key is
generated, was blocked by annex.securehashesonly.

Fixed by passing the Backend that will be used for the final key into
runTransfer. When a Backend is provided, have preCheckSecureHashes
check that, rather than the key being transferred.

Sponsored-by: unqueued on Patreon

Command/CalcKey.hs

@@ -8,7 +8,7 @@
 module Command.CalcKey where
 
 import Command
-import Backend (genKey)
+import Backend (genKey, defaultBackend)
 import Types.KeySource
 import Utility.Metered
 
@@ -21,7 +21,7 @@ cmd = noCommit $ noMessages $ dontCheck repoExists $
 			(batchable run (pure ()))
 
 run :: () -> SeekInput -> String -> Annex Bool
-run _ _ file = tryNonAsync (genKey ks nullMeterUpdate Nothing) >>= \case
+run _ _ file = tryNonAsync (genKey ks nullMeterUpdate =<< defaultBackend) >>= \case
 	Right (k, _) -> do
 		liftIO $ putStrLn $ serializeKey k
 		return True