fix waiting for all started feed downloads with -J

importfeed bug fix: When -J was used with multiple feeds, some feeds did
not get their items downloaded.

In my case, I had added a feed to the end of the list, and no items from it
were ever downloaded.

Sponsored-by: Leon Schuermann on Patreon

Command/ImportFeed.hs

@@ -101,7 +101,7 @@ seek o = startConcurrency commandStages $ do
 					return m
 				else
 					let (pending, rest) = M.partition ispending m
-					in if M.null pending
+					in if M.null pending || not (M.null rest)
 						then retry
 						else do
 							putTMVar dlst rest