fix events with ShouldBroadcastNow

[josiasmontag]

This fix did not completely solve #412.

After dispatching an event with ShouldBroadcastNow the following entries are not correctly associated with the current request.

This PR solves this and disables the premature storing if an event with the sync driver was emitted.

[themsaid]

@josiasmontag I'm not sure what's broken and this PR is trying to fix, what are the steps to re-produce?

[josiasmontag]

class TestEvent implements ShouldBroadcastNow
{
}

class BroadcastTestController extends Controller
{
    public function index(Request $request)
    {
        DB::table('users')->get(); // recoded correctly
        event(new TestEvent());
        DB::table('users')->get() // recorded, but not associated to the current request
    }
}

The second query gets recorded but it does not show up in the "Queries" Tab on the Request detail page in Telescope. This PR solves it and the second query is correctly assigned to the current request.