Warns maybe-uninitialized on g++-6 about fast_float

[biojppm]

There is also this:

opt/jpmag/proj/extern/fast_float/include/fast_float/float_common.h: In constructor ‘fast_float::decimal::decimal()’:
/opt/jpmag/proj/extern/fast_float/include/fast_float/float_common.h:144:3: error: ‘fast_float::decimal::num_digits’ should be initialized in the member initialization list [-Werror=effc++]
   decimal() = default;
   ^~~~~~~
/opt/jpmag/proj/extern/fast_float/include/fast_float/float_common.h:144:3: error: ‘fast_float::decimal::decimal_point’ should be initialized in the member initialization list [-Werror=effc++]
/opt/jpmag/proj/extern/fast_float/include/fast_float/float_common.h:144:3: error: ‘fast_float::decimal::negative’ should be initialized in the member initialization list [-Werror=effc++]
/opt/jpmag/proj/extern/fast_float/include/fast_float/float_common.h:144:3: error: ‘fast_float::decimal::truncated’ should be initialized in the member initialization list [-Werror=effc++]
In file included from /opt/jpmag/proj/extern/fast_float/include/fast_float/parse_number.h:3:0,
                 from /opt/jpmag/proj/extern/fast_float/include/fast_float/fast_float.h:44,
                 from /opt/jpmag/proj/extern/fast_float/tests/long_exhaustive32_64.cpp:1:
/opt/jpmag/proj/extern/fast_float/include/fast_float/ascii_number.h: In function ‘fast_float::decimal fast_float::parse_decimal(const char*, const char*)’:
/opt/jpmag/proj/extern/fast_float/include/fast_float/ascii_number.h:169:11: note: synthesized method ‘fast_float::decimal::decimal()’ first required here 
   decimal answer;
           ^~~~~~

[lemire]

Closed by PR from the submitter.