pdf_get_value for font metrics keys, with font descriptor modifier does not handle the descriptor correctly:

example code :

$pdf = pdf_new();
pdf_open_file($pdf, "");
pdf_begin_page($pdf, 595, 842);
$font = pdf_findfont($pdf, "Times-Roman", "winansi",0); 
pdf_get_value($pdf,'ascender',$font);
pdf_end_page($pdf);
pdf_close($pdf);

output:
Fatal error: PDFlib error: Bad font descriptor 1 in PDF_get_value/descender 

fix: 
pdf_get_value($pdf,'descender',$font-1);

When several fonts are (pre-)loaded, only query to the last one fails. The returned value for the others are probably mixed up. 
PDFlib GmbH Version 4.0.1 
Revision $Revision: 1.79.2.1 $