A table with a font-size and a row with text-rotate throws a TypeError on PHP 8 #632

On PHP 8, a table with a font-size and a row with text-rotate throws a TypeError instead of rendering.

$mpdf = new \Mpdf\Mpdf(['mode' => 'c']);
$mpdf->WriteHTML('<table style="font-size:9pt"><tr style="text-rotate:45"><td>Rotated</td></tr></table>');

TypeError: Unsupported operand types: string / int
src/Mpdf.php:21495, in _tableHeight()

That line is in _tableHeight():

$this->SetFont($c['textbuffer'][0][4], $c['textbuffer'][0][2], $c['textbuffer'][0][11] / $this->shrin_k, true, true);

Index 11 of the cell's first text-buffer entry is the font size, and here it is an empty string. PHP 7 read it as 0, but PHP 8 refuses to divide a string.

• Without the table's font-size, the same document renders.
• With a font-size on the cell as well as the table, it still throws.

Reproduced on gravitypdf at de2a2d4, on PHP 8.5. It was found while testing #535's standard cascade, which reaches this path from TableSnapshotTest.