main/say: Work around gcc 9 format-truncation false positive

Version: gcc (Ubuntu 9.3.0-10ubuntu2) 9.3.0
Warning:
  say.c:2371:24: error: ‘%d’ directive output may be truncated writing
    between 1 and 11 bytes into a region of size 10
    [-Werror=format-truncation=]
  2371 |     snprintf(buf, 10, "%d", num);
  say.c:2371:23: note: directive argument in the range [-2147483648, 9]

That's not possible though, as the if() starts out checking for (num < 0),
making this Warning a false positive.

(Also replaced some else<TAB>if with else<SP>if while in the vicinity.)

Change-Id: Ic7a70120188c9aa525a6d70289385bfce878438a