This case in the "dso_unload" handlers should not be reported as an error -

if a DSO_load(NULL,...) operation fails, it will have to call DSO_free() on
the DSO structure it created and that will filter through to this "unload"
call.

If the stack size is "< 1", then the library never actually loaded. To keep
things clean higher up, I'll treat this as a vacuous case without an error.
It makes the error stack easier to follow real world cases, and the error
this ignores was only useful for catching bugs in internal code, not
mismatched calls from applications (which should be handled in the generic
DSO layer).