Advance cursor after :delete and :move

So that you can repeat the action on the next message if appropriate

commands/account/delete-message.go

@@ -24,6 +24,7 @@ func DeleteMessage(aerc *widgets.Aerc, args []string) error {
 	}
 	store := acct.Messages().Store()
 	msg := acct.Messages().Selected()
+	acct.Messages().Next()
 	store.Delete([]uint32{msg.Uid}, func(msg types.WorkerMessage) {
 		switch msg := msg.(type) {
 		case *types.Done:

commands/account/move.go

@@ -25,6 +25,7 @@ func Move(aerc *widgets.Aerc, args []string) error {
 	}
 	msg := acct.Messages().Selected()
 	store := acct.Messages().Store()
+	acct.Messages().Next()
 	store.Move([]uint32{msg.Uid}, args[1], func(msg types.WorkerMessage) {
 		switch msg := msg.(type) {
 		case *types.Done:

widgets/msglist.go

@@ -109,10 +109,6 @@ func (ml *MessageList) storeUpdate(store *lib.MessageStore) {
 	}
 
 	if len(store.Uids) > 0 {
-		// Prevent selecting beyond the last message
-		for ml.selected >= len(store.Uids) {
-			ml.Prev()
-		}
 		// When new messages come in, advance the cursor accordingly
 		// Note that this assumes new messages are appended to the top, which
 		// isn't necessarily true once we implement SORT... ideally we'd look
@@ -122,6 +118,11 @@ func (ml *MessageList) storeUpdate(store *lib.MessageStore) {
 				ml.Next()
 			}
 		}
+		if len(store.Uids) < ml.nmsgs && ml.nmsgs != 0 {
+			for i := 0; i < ml.nmsgs-len(store.Uids); i++ {
+				ml.Prev()
+			}
+		}
 		ml.nmsgs = len(store.Uids)
 	}