LargeLoadableTypes: fix a corner case with optional function types
Fixes a bug where we have an optional function type for which we changed the signature, and, in addition, gotten said type via a modified struct/enum extract
That is, the function type is contained inside a large loadable type which we transformed into its address variant
There is a check that we have to explode (load instruction) the extract value if it is a function type, however, we did not check if it is an optional function type.