libreoffice/xlsfuzzer: Bad-cast to LogicalFontInstance from invalid vptr in GlyphCache::IFSD_Equal::operator

Detailed report: https://oss-fuzz.com/testcase?key=6241926188630016 Project: libreoffice Fuzzer: libFuzzerlibreofficexlsfuzzer Fuzz target binary: xlsfuzzer Job Type: libfuzzerubsanlibreoffice Platform Id: linux Crash Type: Bad-cast Crash Address: 0x000018c7b2c0 Crash State: Bad-cast to...