Fix[auth]: don't crash if fails to load token from keychain

Natives/authenticator/MicrosoftAuthenticator.m

@@ -217,9 +217,13 @@ typedef void(^XSTSCallback)(NSString *xsts, NSString *uhs);
 - (void)refreshTokenWithCallback:(Callback)callback {
     // Move tokens to keychain if we haven't
     if (!self.tokenData) {
-        [self saveChanges];
+        showDialog(localize(@"Error", nil), @"Failed to load account tokens from keychain");
+        callback(nil, YES);
+        return;
     }
 
+    [self saveChanges];
+
     if ([NSDate.date timeIntervalSince1970] > [self.authData[@"expiresAt"] longValue]) {
         [self acquireAccessToken:self.tokenData[@"refreshToken"] refresh:YES callback:callback];
     } else {