1.x: Fix NULL-pointer dereference when parsing %%PDFTOPDF comments (#644)

1.x: Fix NULL-pointer dereference when parsing %%PDFTOPDF comments (#644)

* Fix null pointer dereference in %%PDFTOPDF* parsers

* %%PDFTOPDFCollate comment parsing: Increment p where needed

Without this, if strchr succeeds, p will point to a ':' character.
*p will therefore never be a whitespace in the subsequent loop,
or compare successfully against the "true" string.