Fix a hang in the send kitten when transmitting deltas of multiple files

and the files have not changed causing the signature of the second file
to arrive after the delta for the first file is transmitted

kittens/transfer/send.go

@@ -834,6 +834,8 @@ func (self *SendHandler) on_file_transfer_response(ftc *FileTransmissionCommand)
 	}
 	if self.manager.all_acknowledged {
 		self.transfer_finished()
+	} else if ftc.Action == Action_end_data && ftc.File_id != "" {
+		return self.transmit_next_chunk()
 	}
 	return nil
 }
@@ -1010,16 +1012,22 @@ func (self *SendManager) next_chunks(callback func(string) loop.IdType) error {
 
 func (self *SendHandler) transmit_next_chunk() (err error) {
 	found_chunk := false
-	err = self.manager.next_chunks(func(chunk string) loop.IdType {
-		found_chunk = true
-		return self.send_payload(chunk)
-	})
-	if err != nil {
-		return err
-	}
-	if !found_chunk {
-		if self.manager.all_acknowledged {
-			self.transfer_finished()
+	for !found_chunk {
+		if err = self.manager.next_chunks(func(chunk string) loop.IdType {
+			found_chunk = true
+			return self.send_payload(chunk)
+		}); err != nil {
+			return err
+		}
+		if !found_chunk {
+			if self.manager.all_acknowledged {
+				self.transfer_finished()
+				return
+			}
+			self.manager.update_collective_statuses()
+			if !self.manager.has_transmitting {
+				return
+			}
 		}
 	}
 	return