p2v: check results of strndup and sscanf
python: fix possible free on uninit memory with OStringList optargs

When using optional arguments of type OStringList, the code free'ing
the member in the optargs_s struct corresponding to that optional
argument would just check for a non-PyNone PyObject for that argument.
If before that optional argument there are other arguments which can
cause an earlier error return from that binding function, the free'ing
code will then act on garbage values.

Enhance the check by also checking whether the optargs struct has the
bitmask with the element for that argument, meaning that the
corresponding struct member was initialized.