OSV-2020-1429 Segv on unknown address in clang::OverloadExpr::find

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=19972 Crash type: Segv on unknown address Crash state: clang::OverloadExpr::find clang::Sema::ResolveAndFixSingleFunctionTemplateSpecialization clang::Sema::CheckPlaceholderExpr...