README-maintaner: sanitize undefined as well as adddress
README-maintaner: sanitize undefined as well as adddress

gcc already warns for undefined variables, but this is in preparation
for Google's oss-fuzz, which builds in this way.

qpdf/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,qpdf/qpdf,qpdf/qpdf,qpdf/qpdf,jberkenbilt/qpdf,qpdf/qpdf,jberkenbilt/qpdf