CppEditor: Tests: Add basic tests for quick fix CompleteSwitchCaseStatement

Change-Id: Idd9773c9f5165ac8a378ee109bf270641a2b3749
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>
CppEditor: Fix crash in CompleteSwitchCaseStatement

Task-number: QTCREATORBUG-10366

Change-Id: I6d5af5e7a59f3867141c8d7f098128d3db532ee5
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>