Attach (recommended) or Link to PDF file here:
[imm5710f(1).pdf](https://github.com/mozilla/pdf.js/files/6924738/imm5710f.1.pdf)

Configuration:
- Web browser and its version: Firefox nightly
- Operating system and its version: Debian

Steps to reproduce the problem:
1. Open the pdf on page 3 
2. See the 2 fields after `DÉTAILS DU TRAVAIL PRÉVU AU CANADA`

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/5641725/128031365-84b17d62-f805-43d1-9d05-e2b535efa3ef.png)

* the initial space.
 * So if the container has known dimensions and these ones are ok with the
 * space then continue else we return HTMLResult.FAILURE: it's up to the
 * parent to deal with this failure (e.g. if parent layout is lr-tb and
 * we fail to add a child at end of line (lr) then we try to add it on the
 * next line).
 * And then we run through the children, each child gets its initial space
 * in calling its parent $getAvailableSpace method
 * (see _filteredChildrenGenerator and $childrenToHTML in xfa_object.js)
 * then we try to layout child in its space. If everything is ok then we add
 * the result to its parent through $addHTML which will recompute the available
 * space in parent according to its layout property else we return
 * HTMLResult.Failure.
 * Before a failure some children may have been layed out: they've been saved in
 * [$extra].children and [$extra] has properties generator and failingNode
 * in order to save the state where we were before a failure.
 * This [$extra].children property is useful when a container has to be splited.
 * So if a container is unbreakable, we must delete its [$extra] property before
 * returning.
 */
function createLine(node, children) {
  return {
    name: "div",
    attributes: {
      class: [node.layout === "lr-tb" ? "xfaLr" : "xfaRl"],
    },
    children,
  };
}
function flushHTML(node) {