b2b_logic: Fix pkg_str_dup ret code check

Fix bug while checking the return of pkg_str_dup - due to the bad return
check, we were no longer terminating dangling entities with BYE.

Many thanks to David Escartin from Sonoc for reporting and help in
troubleshooting this issue!

modules/b2b_logic/b2b_logic.c

@@ -718,7 +718,7 @@ static void term_entity(b2bl_entity_id_t *entity, int hash_index, str *key)
 	} else {
 		if ( key && ( !push_new_global_context() ||
 		(ctx=b2b_api.get_context())==NULL ||
-		pkg_str_dup(&ctx->b2bl_key, key)==0 )
+		pkg_str_dup(&ctx->b2bl_key, key)!=0 )
 		) {
 			LM_ERR("preparing ctx for request failed, entity [%.*s]\n",
 				entity->key.len, entity->key.s);