[PATCH 4/4] comctl32/imagelist: Make ImageList_Destroy just decrease refcount. Move actual destruction to ::Release.

[Nikolay Sivov]

Currently ImageList_Destroy corrupts imagelist data releasing all fields even if it's
still referenced. This patch moves release part to IUnknown_Release() and make
ImageList_Destroy just check for valid imagelist. Also vtable field is reset to NULL
as suggested by Alexandre.

This patch depends on my recent series, so it should be applied after it.