Fixed the crash appears after closing app when use ResizePolicy::USE_NATURAL_SIZE

Fixed the crash appears after closing app when use ResizePolicy::USE_NATURAL_SIZE

There is a crash when destroying text-editor and the ResizePolicy is USE_NATURAL_SIZE.

textEditor.SetProperty(Dali::Actor::Property::WIDTH_RESIZE_POLICY, ResizePolicy::USE_NATURAL_SIZE);"
then close the application. the below exception appears.
ERROR: DALI: Assert (threadLocal) failed in: static Dali::Internal::ThreadLocalStorage& Dali::Internal::ThreadLocalStorage::Get()
Exception:
threadLocal
 thrown at static Dali::Internal::ThreadLocalStorage& Dali::Internal::ThreadLocalStorage::Get()
terminate called after throwing an instance of 'Dali::DaliException'

The solution applied at RelayoutController::Get().
Checked if ThreadLocalStorage is created then proceed normally otherwise returns null
Because the ThreadLocalStorage::Get() only retrieves STL without checking if it exists.

The caller of RelayoutController::Get() should check if RelayoutController is not null.
There is only one place use this function and already checks if RelayoutController is not null.

Change-Id: I343ef47f03aa86babb4bdd19f95c3e7ccb211dff