User can't connect if acl_file contains no username block

[quonb]

If acl_file contains only pattern rules or there is no definition for user then acl__find_acls function returns MOSQ_ERR_INVAL.

mosquitto/src/security_default.c

Lines 645 to 647 in 6b43ba8

	if(context->username && context->acl_list == NULL){
	return MOSQ_ERR_INVAL;
	}

This causes immediate disconnect despite correct username/password pair

mosquitto/src/handle_connect.c

Lines 614 to 615 in 6b43ba8

	rc = acl__find_acls(db, context);
	if(rc) return rc;

This regression were caused by c40957a

[ralight]

Thanks for finding this. For information, the description isn't quite right, it only happens if the anonymous ACL list is defined but there are no specific user ACLs. I've pushed a fix to the fixes branch.