Implicit `bool` conv. for `if (args)` checking about args

[xparq]

From the code:

bool operator !() const { return argc < 2; }
//!!	operator bool() const { return !!*this; }
//! Enabling op bool would break args["opt"] due to a weird ambiguity, where the
//! compiler would suddenly think it may also match the builtin "opt"[int]! :-o
//! It's due to it trying a match with autoconverted bool->int before the "real thing".
//! The hacky workaround below may be good enough tho (but certainly not "good":
//! -> https://www.artima.com/articles/the-safe-bool-idiom)
//! Just comment it out, if you feel offended! ;)
operator const void*() const { return !(*this) ? nullptr : (void*)this; }