Constraint with centerX/centerY seems lead to random crash

[thorfei]

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Issue Info

Info	Value
Platform	ios
Platform Version	7.0/8.0/9.0
Masonry Version	1.0.2
Integration Method	cocoapods

Issue Description

Our app got random with using centerY or centerX attribute like below code snippets. And we try don't use them, no crash collected. We read the masonry source code, and have no idea about the crash reason. This random crash is hard to reproduce because of memory issue.

Anybody else met the same crash let me know！

[checkIcon makeConstraints:^(MASConstraintMaker *make) {
        make.centerY.equalTo(container.centerY); // random crash
        make.left.equalTo(container.left).offset(15.0f);
        make.width.and.height.equalTo(20.0f);
 }];

 [textLabel makeConstraints:^(MASConstraintMaker *make) {
    __strong typeof(wself) self = wself;
    make.centerY.equalTo(self.centerY); // random crash
    make.leading.equalTo(self.leading).offset(15);
}];

[button makeConstraints:^(MASConstraintMaker *make) {
    make.centerY.equalTo(nicknameTextField.centerY); // random crash
    make.width.height.equalTo(17.0f);
    make.right.equalTo(self).offset(-12.5);
}];

[containerView makeConstraints:^(MASConstraintMaker *make) {
    make.centerX.equalTo(contentView.centerX).offset(2); //random crash
    make.centerY.equalTo(contentView.centerY);
}];

Crash stack like this

#0. Crashed: com.apple.main-thread
0  libobjc.A.dylib                0x3954e608 objc_retain + 7
1  xxx                            0x1c31ed __30-[YYView layout]_block_invoke (PDDChatListLoginView.m:66)
2  xxx                            0x4479cb -[UIView(MASAdditions) mas_makeConstraints:] (View+MASAdditions.m:17)
3  xxx                            0x1c2fb5 -[YYView layout] (YYView.m:64)
4  xxx                            0x1c2ab3 -[YYView initWithFrame:] (YYView.m:32)