Panic when table has an empty heading cell

[rahji]

A table like this:

|       | head2 | head3 |
| ----- | ----- | ----- |
| 1     | 2     | 3     |

causes a panic. As far as I know, it's legal markdown to have an empty heading cell, but not sure. I've never had a problem rendering it in any other way or converting it to PDF with pandoc, vscode extensions, etc.