Fix findTransitiveUsesForAddress to handle incomplete scopes
This fixes ScopedAddressValue::computeLiveness in unreachable code scenarios.
For example:
%storeBorrow = store_borrow %_ to %adr
%loadBorrow = load_borrow %storeBorrow
apply %f(%loadBorrow) : $@convention(thin) (...) -> Never
Now recursively process uses of load_borrow as if they are address
uses.
Ultimately, this would be more efficiently handled by a recursive
lifetime completion utility which would fixup the load_borrow scope
before computing the store_borrow liveness.
Fixes rdar://99874173: unreachable assert "No user in LiveWithin block"
