refreshSession shouldn't fail because currentSession doesn't exists if the refreshToken is provided

[Aadim1]

Describe the bug
Much like the title, I don't think this is a correct behavior, mostly because supabase-flutter is already doing this Nullish coalescing check anyway.

Future<AuthResponse> refreshSession([String? refreshToken]) async {
    if (currentSession?.accessToken == null) {
      _log.warning("Can't refresh session, no current session found.");
      throw AuthSessionMissingException();
    }
    _log.info('Refresh session');

    final currentSessionRefreshToken =
        refreshToken ?? _currentSession?.refreshToken;

    if (currentSessionRefreshToken == null) {
      throw AuthSessionMissingException();
    }

    return await _callRefreshToken(currentSessionRefreshToken);
  }

This code snippets, realistically only needs this piece of code:

if (currentSessionRefreshToken == null) {
      throw AuthSessionMissingException();
    }

The first one doesn't seem right to me. That check is also not doing anything, and blocks a valid use-case where you might have a refreshToken but no current session atm.

[grdsdev]

Hey @Aadim1 thanks for reporting this.

I think this is a valid ask, I'll put this in our backlog.

If someone from the community wants to pick this, I think we can just mimic JS behavior as defined in https://github.com/supabase/supabase-js/blob/master/packages/core/auth-js/src/GoTrueClient.ts#L1894