Fix undefined-behavior in smc_keys strtoul
Fix undefined-behavior in smc_keys strtoul

Issue highlighted by asan activated in PR osquery/osquery#5628

When shifting left or right a byte, that must be positive, so
ensure it is.

Light cleanup of a bugged and unused function.
A deeper look into the table implementation is needed.

PR: osquery/osquery#5665

hackgnar/osquery,hackgnar/osquery,hackgnar/osquery