Intel C++ Compiler 17.0 produces compilation warning

[dmitrygx]

Intel C++ Compiler 17.0 concerned about missing return statement at the end of function:
cpprest\json.h(1398): warning #1011: missing return statement at end of non-void function "web::json::number::operator=="

That's not a problem, because program will be aborted in _assume(0); statement, but it will be pretty nice to suppress this kind of compilation warning.

[ras0219-msft]

Fixed by #454, thanks!