Correctly update mino2

When we've already seen a trimix gas, of we after that see a nitrox gas
with less o2, it shouldn't update the mino2 state.

Signed-off-by: Anton Lundin <glance@ac2.se>

core/divelist.c

@@ -47,7 +47,7 @@ void get_dive_gas(const struct dive *dive, int *o2_p, int *he_p, int *o2max_p)
 			continue;
 		if (o2 > maxo2)
 			maxo2 = o2;
-		if (o2 < mino2)
+		if (o2 < mino2 && maxhe <= 0)
 			mino2 = o2;
 		if (he > maxhe)
 			goto newmax;