Fully order NaN

NaN is unordered in IEEE754, but we need all values to be ordered.
Make NaN larger than any other float (including inf) so that
dicts with NaN keys work correctly.

Signed-off-by: Keith Packard <keithp@keithp.com>

snek-poly.c

@@ -87,6 +87,9 @@ snek_poly_cmp(snek_poly_t a, snek_poly_t b, bool is)
 	int sdiff;
 	switch (atype) {
 	case snek_float:
+		tdiff = snek_is_nan(a) - snek_is_nan(b);
+		if (tdiff)
+			return tdiff;
 		return (b.f < a.f) - (a.f < b.f);
 	case snek_string:
 		sdiff = strcmp(snek_poly_to_string(a), snek_poly_to_string(b));