Panic when parsing long float

[dtolnay]

json::parse("2.22507385850720113605740979670913197593481954635164564e-308").unwrap();

thread 'main' panicked at 'attempted to add with overflow', /home/david/.cargo/git/checkouts/json-rust-8fc837b9d242b7ce/0.8.5/src/parser.rs:401

This is on the 0.8.5 branch.

[maciejhirsz]

Aye, I'm aware, left myself a comment :)

            // FIXME: prevent overflowing!
            read_num!(self, digit, {
                f = (f << 1) + (f << 3) + digit as u64;
                p = (p << 1) + (p << 3);
            });