Fixes iter error in FAISS add_embeddings call (#5367)
# Remove re-use of iter within add_embeddings causing error
As reported in https://github.com/hwchase17/langchain/issues/5336 there
is an issue currently involving the atempted re-use of an iterator
within the FAISS vectorstore adapter
Fixes # https://github.com/hwchase17/langchain/issues/5336
## Who can review?
Community members can review the PR once tests pass. Tag
maintainers/contributors who might be interested:
VectorStores / Retrievers / Memory
- @dev2049
