Vault cannot be upgraded

### Description

I downloaded the latest version and it told me I need to upgrade my vaults to a new format before I can access them. I clicked upgrade vault and it takes pretty long until it crashed with the following error:

```
java.nio.file.FileSystemException: xx:\My Drive\xx\d\6C\xxxxxxxxxxxx: Insufficient system resources exist to complete the requested service
at java.base/sun.nio.fs.WindowsException.translateToIOException(Unknown Source)
at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(Unknown Source)
at java.base/sun.nio.fs.WindowsDirectoryStream.(Unknown Source)
at java.base/sun.nio.fs.WindowsFileSystemProvider.newDirectoryStream(Unknown Source)
at java.base/java.nio.file.Files.newDirectoryStream(Unknown Source)
at java.base/java.nio.file.FileTreeWalker.visit(Unknown Source)
at java.base/java.nio.file.FileTreeWalker.next(Unknown Source)
at java.base/java.nio.file.Files.walkFileTree(Unknown Source)
at org.cryptomator.cryptofs.migration.v7.Version7Migrator.migrate(Version7Migrator.java:80)
at org.cryptomator.cryptofs.migration.Migrators.migrate(Migrators.java:112)
at org.cryptomator.ui.migration.MigrationRunController.lambda$migrate$2(MigrationRunController.java:113)
at org.cryptomator.ui.common.Tasks$TaskImpl.call(Tasks.java:140)
at javafx.concurrent.Task$TaskCallable.call(Task.java:1425)
at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.base/java.lang.Thread.run(Unknown Source)
```

### System Setup

* Win 10
* Cryptomator version: 1.5.13
* Volume type: Dokany

### Steps to Reproduce

Well I didn't use my vault for a while and downloaded the latest version which now fails to run the upgrades.

#### Expected Behavior

The vault upgrade to work and later to use my vaults again.

#### Actual Behavior

The upgrade crashes with the error msg from above.

#### Reproducibility

[Always/Intermittent/Only once]

### Additional Information

Log file shows the error msg from above. Happy to provide more info if needed.

Thanks

Start by reproducing the upgrade on Windows 10 with a Dokany vault, then inspect the failure at org.cryptomator.cryptofs.migration.v7.Version7Migrator.java:80 and the migration calls in Migrators.java:112. Check how the migration reaches MigrationRunController.java:113 and verify that the vault upgrade completes without the reported FileSystemException.

Written by the indexing model from the issue text.