Wrong sync filter is used if startClient called when cannot connect to server

e.g. when offline

As the `getVersions()` call fails, and this is used to build the feature support matrix which sync.ts needs to `buildDefaultFilter` - leading to potentially not using the new filter needed for some threads features to work properly.

Start in sync.ts at buildDefaultFilter and trace how startClient obtains versions through getVersions() when the server cannot be reached. Check how the feature support matrix is used to select the sync filter, then verify that the appropriate filter remains available when getVersions() fails, including the thread features mentioned in the issue.

Written by the indexing model from the issue text.