Change pagenum arguments in PDFDoc::markAnnotations from Guint to int

Bug #79410
Fixes compile warning:

  CXX      PDFDoc.lo
PDFDoc.cc: In member function 'GBool PDFDoc::markAnnotations(Object*, XRef*, XRef*, Guint, Guint, Guint)':
PDFDoc.cc:1607:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
               if (obj2.getRef().num == oldPageNum) {
                                        ^
PDFDoc.cc:1617:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
               } else if (obj2.getRef().num == newPageNum) {

https://bugs.freedesktop.org/show_bug.cgi?id=79410