野指针crash

[liulei6415]

UIView+LookinServer.m
- (NSArray<LookinAutoLayoutConstraint *> *)lks_constraints {
...
LookinConstraintItemType firstItemType = [self _lks_constraintItemTypeForItem:constraint.firstItem];
LookinConstraintItemType secondItemType = [self _lks_constraintItemTypeForItem:constraint.secondItem];
...
}

这里使用的firstItem secondItem 在 NSLayoutConstraint 用的assign修饰的，不安全属性，真机调试的时候会产生野指针错误。

尝试对constraint.active做了一下判断，非激活态就过就将约束滤掉，观察了一段时间不在crash，目前没有发现副作用，不知道可不可以这样修复一下。

   NSArray<LookinAutoLayoutConstraint *> *lookinConstraints = [self.lks_involvedRawConstraints lookin_map:^id(NSUInteger idx, __kindof NSLayoutConstraint *constraint) {
        BOOL isEffective = [effectiveConstraints containsObject:constraint];
        if ([constraint isActive]) {
            LookinConstraintItemType firstItemType = [self _lks_constraintItemTypeForItem:constraint.firstItem];
            LookinConstraintItemType secondItemType = [self _lks_constraintItemTypeForItem:constraint.secondItem];
            LookinAutoLayoutConstraint *lookinConstraint = [LookinAutoLayoutConstraint instanceFromNSConstraint:constraint isEffective:isEffective firstItemType:firstItemType secondItemType:secondItemType];
            return lookinConstraint;
        }
        return nil;
    }];