Log: establish correct character string literals also with qb_logt sink

Immediate follow-up for 29618ef63 (observation of that issue provoked
this very catch-all iteration), and thematically for fc87717a9.

Note that as in the latter case, this discovery was also enabled with
a special instrumentation at the libqb's side, but this time around,
it wasn't so straightforward:
<INSERT PR LINK HERE>