Fix ASAN heap-buffer-overflow issue on GetNaturalSize()

Fix ASAN heap-buffer-overflow issue on GetNaturalSize()

CSharp_Dali_Actor_GetSuggestedMinimumWidth/Height calls
GetNaturalSize().
This causes ASAN heap-buffer-overflow issue when
SwigDirector_ViewWrapperImpl::GetNaturalSize() is called.

In SwigDirector_ViewWrapperImpl::GetNaturalSize(), type casting from
Dali::Vector2 to Dali::Vector3 is done so it causes ASAN
heap-buffer-overflow issue.

Not to cause ASAN heap-buffer-overflow issue, casting Dali::Vector2 and
assigning it to Dali::Vector3 is required.

Change-Id: I1a85da7440c517f5cd27c32b535359d670b57655