Fixed retval handling after an exception.

Fixed retval handling after an exception.

Previously, some functions set a retval too early.  If this happened
before an exception a partially created object in inconsistent state
may be visible outside the affected functions.

The following functions were fixed:
Object.prototype.valueOf()
Array.prototype.toSpliced()
Array.prototype.toReversed()
Array.prototype.toSorted()

This fixes #713 issue on Github.