Bug 1070429 - [email/IMAP] premature saving leads to missing bodies

If the results[key] value is a string, would this be an incorrect match? Perhaps an Array.isArray() check on the args? This causes a ripple effect for where the value is just `arguments` as in allbackMaker though. Array.isArray(arguments) is false, so likely need to slice(arguments) to lock this down.

A `typeof errIfAny !== 'string'` may be enough for this hazard, and cheaper as far as generating more arrays to garbage collect, but making sure the result value is a true array via slice generally seems better, in case other consumers decide to do some similar check.