pulse-server: handle if the module is destroyed while loading

Create a new event for modules ('destroy') which is emitted from
`module_free()`. It is used by the module loading logic, to handle
when a module is destroyed without properly loading first.

src/modules/module-protocol-pulse/module.c

@@ -92,6 +92,8 @@ void module_free(struct module *module)
 {
 	struct impl *impl = module->impl;
 
+	module_emit_destroy(module);
+
 	if (module->idx != SPA_ID_INVALID)
 		pw_map_remove(&impl->modules, module->idx & INDEX_MASK);