Show understandable error message if the vault.cryptomator-file is missing in vault version 8

[SailReal]

Please agree to the following

• I have searched existing issues for duplicates
• I agree to follow this project's Code of Conduct

Summary

As a user, I want to get a better error message if my vault.cryptomator file is missing

System Setup

- Android: x
- Cryptomator: 1.6.3

Cloud Type

No response

Steps to Reproduce

1. Create a vault using Cryptomator 1.6.x
2. Delete vault.cryptomator
3. Unlock vault

Expected Behavior

User knows, that the vault.cryptomator file is missing

Actual Behavior

Reproducibility

Always

Relevant Log Output

D	20211111220706.532	UnlockVaultUsingMasterkeyUseCase	started 10d1eea7
D	20211111220707.075	UnlockVaultUsingMasterkeyUseCase	failed 10d1eea7
D	20211111220707.077	ExceptionHandler	Unexpected error
org.cryptomator.cryptolib.api.UnsupportedVaultFormatException: Tried to open vault of version 999, but can only handle version 7
	at org.cryptomator.data.cloud.crypto.MasterkeyCryptoCloudProvider.assertLegacyVaultVersionIsSupported(MasterkeyCryptoCloudProvider.kt:210)
	at org.cryptomator.data.cloud.crypto.MasterkeyCryptoCloudProvider.unlock(MasterkeyCryptoCloudProvider.kt:109)
	at org.cryptomator.data.cloud.crypto.CryptoCloudFactory.unlock(CryptoCloudFactory.java:68)
	at org.cryptomator.data.repository.CloudRepositoryImpl.unlock(CloudRepositoryImpl.java:110)
	at org.cryptomator.domain.usecases.vault.UnlockVaultUsingMasterkey.execute(UnlockVaultUsingMasterkey.java:42)
	at org.cryptomator.domain.usecases.vault.UnlockVaultUsingMasterkeyUseCase$Launcher$2.call(UnlockVaultUsingMasterkeyUseCase.java:117)
	at org.cryptomator.domain.usecases.vault.UnlockVaultUsingMasterkeyUseCase$Launcher$2.call(UnlockVaultUsingMasterkeyUseCase.java:111)
	at io.reactivex.internal.operators.flowable.FlowableFromCallable.subscribeActual(FlowableFromCallable.java:39)
	at io.reactivex.Flowable.subscribe(Flowable.java:14935)
	at io.reactivex.Flowable.subscribe(Flowable.java:14882)
	at io.reactivex.internal.operators.flowable.FlowableSubscribeOn$SubscribeOnSubscriber.run(FlowableSubscribeOn.java:82)
	at io.reactivex.internal.schedulers.ExecutorScheduler$ExecutorWorker$BooleanRunnable.run(ExecutorScheduler.java:288)
	at io.reactivex.internal.schedulers.ExecutorScheduler$ExecutorWorker.run(ExecutorScheduler.java:253)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
	at java.lang.Thread.run(Thread.java:923)

ErrorCode: HDT2:CS1T

Anything else?

Due to the fact, that the vault version is 999, we know that there must exists a vault.cryptomator file

[SailReal]

Fixed in 0fc53f9