Assertion on output with m_value = -2147483648

[Klummel69]

The following test code leads to an assertion

fpm::fixed_16_16 x {fpm::fixed_16_16::from_raw_value(-2147483647 - 1) };
std::cout << x << std::endl;

Message: Assertion failed!
File: fpm/ios.hpp, Line 99
Expression: value.raw >= 0

Reason in Line91: value.raw = -value.raw; not possible for INT32_MIN.