Fix needed for FC6

+++ This bug was initially created as a clone of Bug #194363 +++

tiff2pdf buffer overflow

A buffer overflow flaw has been found in tiff2pdf.
Thomas Biege told vendor-sec about this (it came from a colleague of
his)

The code in question is as such:

char buffer[5];
...
sprintf(buffer, "\\%.3o", pdfstr[i]);


pdfstr[i] is signed char, therefore would write \37777777741


This issue also affects FC4