Cache member in SetMemberCache

SetMemberCache was no longer caching the member passed to it. This was causing performance problems, in which a script was taking 3-4 times longer to run than without proper caching. There was a missing line SetMemberCache which fixed the issue.

A concern with this change is the offending line was removed during a refactor, in which the commit message said "fixing generic exceptions". I do not know which generic exceptions were fixed during that commit, and don't know if breaking caching, or removing this line was intentional.