Accept xref streams with the type field not present.

[olpa]

pyPdf can't parse a cross-reference stream unless the whole triple is given for its entries. But at least from PDF 1.6:

A value of zero for an element in the W array indicates that the corresponding field is not present in the stream, and the default value is used, if there is one. If the first element is zero, the type field is not present, and it defaults to type 1.