Merge pull request #488 from onflow/bastian/unreachable-guard-else-end

Defensively panic when end of a guard's else branch is reached by interpreter

Merge pull request #461 from onflow/fxamacker/bump-atree-verison-to-v…

…0.15.0

Bump to atree v0.15 and fxamacker/cbor v2.9.1 stream-mode branch

Update ReadOnlyLoadedValueIterator() to return DomainStorageMapIterator