Attach (recommended) or Link to PDF file here:
http://education.ohio.gov/getattachment/Topics/Special-Education/Preschool-Special-Education/ETR-Preschool-Planning-Form.pdf.aspx

- Web browser and its version: Firefox 89.0.1
- Operating system and its version: Windows 10 10.0.19043.1052
- PDF.js version: commit 5d251a3a3e7bfaa8fbfa07f0b7f9901eb3f999d9
- Is a browser extension: No

Steps to reproduce the problem:
1. Enable XFA support
2. Open form

What is the expected behavior? (add screenshot)
Shapes stay inside table cells
![image](https://user-images.githubusercontent.com/7104454/122572782-1252a580-d01c-11eb-9d0f-5fed46d6f2fe.png)

What went wrong? (add screenshot)
Shapes fall outside cells (among other issues)
![image](https://user-images.githubusercontent.com/7104454/122572885-2d251a00-d01c-11eb-8863-fa3b9969f0ea.png)

if (!this.value) {
      return HTMLResult.EMPTY;
    }
    const value = this.value[$toHTML](availableSpace).html;
    if (!value) {
      return HTMLResult.EMPTY;
    }
    const savedReserve = this.reserve;
    if (this.reserve <= 0) {
      const { w, h } = this[$getExtra](availableSpace);
      switch (this.placement) {
        case "left":
        case "right":
        case "inline":
          this.reserve = w;
          break;
        case "top":
        case "bottom":
          this.reserve = h;
          break;
      }
    }
    const children = [];
    if (typeof value === "string") {
      children.push({
        name: "#text",
        value,
      });
    } else {