module: postpone lt_dlclose() until a safe time

module: postpone lt_dlclose() until a safe time

When unloading a module, lt_dlclose() may remove the module from memory.
If a module unloads itself, it's not safe to call lt_dlclose()
synchronously from pa_module_unload(), because the execution may return
to the module code that was removed from memory. To avoid this
situation, let's postpone lt_dlclose() until it's safe to call it.

BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=96831