In a28e23d900, we said:
The callbacks will be called repeatedly, once with data, and later
on with eol == 0. Make sure to only free it when we get the eol call
instead of once we've applied the settings.
Whereas the docs say:
When requesting all of these [instances] at once, the callback will be
called multiple times, once for each object. When the list has been
exhausted, the callback will be called without an information structure
and the eol parameter set to a positive value.
If an error occurs, the callback will be invoked without an information
structure and eol set to a negative value.
So, in all, we need to free our callback data when eol is positive, or
negative. So, when it's not 0.
Seems we got lucky in the original commit because the test machine only
had a single soundcard.
25bf3ed75f