ncd: NCDModule: allow func_die to be set to NULL, and default to calling NCDModuleInst_Backend_Dead().

ncd/NCDModule.c

@@ -98,6 +98,11 @@ static void die_job_handler (NCDModuleInst *n)
     
     n->state = STATE_DYING;
     
+    if (!n->m->func_die) {
+        NCDModuleInst_Backend_Dead(n);
+        return;
+    }
+    
     n->m->func_die(n->inst_user);
     return;
 }

ncd/NCDModule.h

@@ -626,6 +626,7 @@ struct NCDModule {
     
     /**
      * Function called to request termination of a backend instance.
+     * May be NULL, in which case the default is to call NCDModuleInst_Backend_Dead().
      */
     NCDModule_func_die func_die;