OSV-2020-1850 Heap-buffer-overflow in fmt::v6::basic_string_view<char>::basic_string_view

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=21763 Crash type: Heap-buffer-overflow READ 2 Crash state: fmt::v6::basicstringview::basicstringview fmt::v6::basicformatargfmt::v6::basicformatcontextstd::1::backinsertit...