title: Auto layout internal error happening when a view is dismissed
body: <p>I'm getting a funny error when I dismiss some views on which I have some constraints.</p>
  
  <blockquote>
    <p>Auto layout internal error.  Cannot find an outgoing row head for
    incoming head AppName.ViewName:0x7fc072ed8ef0.Width{id: 6805} during
    optimization of variable with near-zero coefficient, which should
    never happen.</p>
  </blockquote>
  
  <p>I'm getting this bug on several views to which I'm adding these constraints. One variation of this error message is the following: </p>
  
  <blockquote>
    <p>Auto layout internal error.
    Cannot find an outgoing row head for incoming head {id: 6630} during optimization of
    variable with near-zero coefficient, which should never happen.</p>
  </blockquote>
  
  <p>Has anyone experienced similar issues with this error? Any tips on how to debug it?</p>