prf.c: properly format INF/NAN/zero with prefix

The space or plus prefix must appear when requested even with INF and
NAN. And no zero-padding in that case.

Also, 0.0 and -0.0  are distinct values. It is necessary to display
the minus sign with a negative zero.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
2 files changed