OSV-2020-1495 Segv on unknown address in clang::ObjCMethodDecl::getOverriddenMethods

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19086 Crash type: Segv on unknown address Crash state: clang::ObjCMethodDecl::getOverriddenMethods clang::ObjCMethodDecl::findPropertyDecl clang::Sema::DiagnoseUseOfDecl...