Assignment operator does not check for self-assignment

Defect 73462 (STATIC_C)
Checker SELF_ASSIGN (subcategory none)
File: /src/mongo/util/net/message.h
Function mongo::Message::operator =(mongo::Message&&)
/src/mongo/util/net/message.h, line: 420
No protection against the object assigning to itself.

            _buf = r._buf;