Deno.core.evalContext() crashes & Deno.core.print() crashes fix

[mhvsa]

Regarding #2457 and #2458

Now it's throwing a catchable error.

> Deno.core.evalContext();

Uncaught TypeError: Invalid Argument
    at <unknown>:1:11
    at evaluate (js/repl.ts:87:34)
    at replLoop (js/repl.ts:145:13)

> Deno.core.print();

Uncaught TypeError: Invalid Argument
    at <unknown>:1:11
    at evaluate (js/repl.ts:87:34)
    at replLoop (js/repl.ts:145:13)

[CLAassistant]

All committers have signed the CLA.

[ry]

LGTM - thanks!