scanner: Allow disabling weak hash in scanning (fixes #3891)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3905

cmd/stfileinfo/main.go

@@ -70,7 +70,7 @@ func main() {
 		if *standardBlocks || blockSize < protocol.BlockSize {
 			blockSize = protocol.BlockSize
 		}
-		bs, err := scanner.Blocks(fd, blockSize, fi.Size(), nil)
+		bs, err := scanner.Blocks(fd, blockSize, fi.Size(), nil, true)
 		if err != nil {
 			log.Fatal(err)
 		}