new gcc 7.0.1 warnings

Hi

I am checking new Fedora 26, where new gcc compiler is used.

float.c: In function ‘float4out’:
float.c:382:41: warning: ‘%.*g’ directive output may be truncated writing
between 1 and 310 bytes into a region of size 65 [-Wformat-truncation=]
snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);
^~~~
float.c:382:5: note: ‘snprintf’ output between 2 and 311 bytes into a
destination of size 65
snprintf(ascii, MAXFLOATWIDTH + 1, "%.*g", ndig, num);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
float.c: In function ‘float8out_internal’:
float.c:618:42: warning: ‘%.*g’ directive output may be truncated writing
between 1 and 310 bytes into a region of size 129 [-Wformat-truncation=]
snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);
^~~~
float.c:618:5: note: ‘snprintf’ output between 2 and 311 bytes into a
destination of size 129
snprintf(ascii, MAXDOUBLEWIDTH + 1, "%.*g", ndig, num);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Regards

Pavel