Fatal Error triggered when previewing templates when using characters such as é

[markcummins]

Steps to Reproduce

1. Go to the backend and create a new certificate template
2. Set the 'Certified Message' field to be 'This is to certify that é has completed the course'
3. Preview the certificate
4. See the 'Fatal Error' wp error message

What's happening is that first of all, in class-woothemes-sensei-certificate-templates.php, it sees that the font has a weird character set, and it returns 'mb'.

Then it sets the font to 'Deja Vu', because the font type is 'mb'

// Set the field text styling based on the font type
$fonttype = '';
if (!$custom_font) {
	$fonttype = $this->get_font_type($value);
	switch ($fonttype) {
	        case 'mb':
			$fpdf->SetFont('DejaVu', '', $font['font_size']);
			break;
		case 'latin':
			$fpdf->SetFont($font['font_family'], $font['font_style'], $font['font_size']);
			break;
		default:
			$fpdf->SetFont($font['font_family'], $font['font_style'], $font['font_size']);
			break;
	}
}

Then in '/sensei-certificates/lib/tfpdf/tFPDF/PDF.php', it triggers the fatal error, because 'DejaVu' is not in the arr_core_fonts array

if (in_array($str_family, $this->arr_core_fonts)) {
    if ($str_family == 'symbol' || $str_family == 'zapfdingbats') {
        $str_style = '';
    }
    $str_font_key = $str_family . $str_style;
    if (!isset($this->arr_fonts[$str_font_key])) {
        $this->AddFont($str_family, $str_style);
    }
} else {
    $this->Error('Undefined font: ' . $str_family . ' ' . $str_style);
}