libreoffice/slkfuzzer: Bad-cast to ScPoolHelper from invalid vptr in ScDocument::GetDefPattern

Project: git://anongit.freedesktop.org/libreoffice/core Detailed report: https://oss-fuzz.com/testcase?key=5728793961955328 Project: libreoffice Fuzzer: libFuzzerlibreofficeslkfuzzer Fuzz target binary: slkfuzzer Job Type: libfuzzerubsanlibreoffice Platform Id: linux Crash Type: Bad-cast Crash...