Fix save_credential failing when the selected cipher doesn't have a P…

…asskey (#831)

## 🎟️ Tracking

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## 📔 Objective

The current call to `get_selected_credential` inside `save_credential`
will try to fetch and decrypt the ciphers FIDO2 credentials, and error
if they are not there.

This can only happen when creating a new Passkey, so instead of calling
`get_selected_credential` we just get the value from the lock. The other
places where `get_selected_credential` is used is in `update_credential`
and right at the end of the `assertion`, `register` and `authenticate`
operations, so those should be safe.

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- Protected functional changes with optionality (feature flags)
- Used internationalization (i18n) for all UI strings
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- Updated any necessary documentation (Confluence, contributing docs) or
informed the documentation
  team

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---------

Co-authored-by: Andreas Coroiu <andreas.coroiu@gmail.com>

crates/bitwarden/src/platform/fido2/authenticator.rs

@@ -311,7 +311,14 @@ impl passkey::authenticator::CredentialStore for CredentialStoreImpl<'_> {
             let cred = try_from_credential_full(cred, user, rp)?;
 
             // Get the previously selected cipher and add the new credential to it
-            let mut selected: CipherView = this.authenticator.get_selected_credential()?.cipher;
+            let mut selected: CipherView = this
+                .authenticator
+                .selected_credential
+                .lock()
+                .expect("Mutex is not poisoned")
+                .clone()
+                .ok_or("No selected cipher available")?;
+
             selected.set_new_fido2_credentials(enc, vec![cred])?;
 
             // Store the updated credential for later use