buffer overflows in to_chars for std::bfloat16_t

[gpeterhoff]

Hi Matt,
if the buffer is too small and value = ±inf/±(s)nan there will be buffer overflows again. Here:

using buffer_type = std::array<char, 2>;
value = -L::quiet_NaN();

std::bfloat16_t
(std  , scientific)	{}	(2, Value too large for defined data type)
(boost, scientific)	BOF!	(9, Success)

(std  , fixed     )	{}	(2, Value too large for defined data type)
(boost, fixed     )	BOF!	(9, Success)

(std  , hex       )	{}	(2, Value too large for defined data type)
(boost, hex       )	{}	(2, Numerical result out of range)

(std  , general   )	{}	(2, Value too large for defined data type)
(boost, general   )	BOF!	(9, Success)

regards
Gero