lparser.c:singlevar() asserts potentially uninitialised value.

[Duane Leslie <parakleta@...>]

In lparser.c function `singlevar()` it checks that the `ls->envn`
named variable (i.e. _ENV) is initialised to a VLOCAL or VUPVAL, but
the `singlevaraux()` function may return VVOID without ever
initialising the `var->k` value.  The assert should be instead that
`singlevaraux()` doesn't return VVOID.

Regards,

Duane.