OSV-2021-1099 Stack-buffer-overflow in ot::StringFind

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=36830 Crash type: Stack-buffer-overflow READ 1 Crash state: ot::StringFind ot::Coap::Message::AppendUriPathOptions otCoapMessageAppendUriPathOptions...