binary_reader.hpp:650: (style) Unsigned expression 'mant' can't be negative so it is unnecessary to test it

https://github.com/Xav83/nlohmann-json-cppcheck/commit/910a7d2b873dd7ae92ec81cced2bf73200ff4848/checks#step:5:84Signed-off-by: Xav83 <x.jouvenot@gmail.com>