Use neutral color for "no SAC information"

In commit 31d1d1f4217c ("Don't change pen color when for zero SAC") Robert
continues to use the last SAC color (which certainly was better than
switching to dark green for "extremely low SAC rate"). But I think it
makes even more sense to mark it as neutral - so I picked a gray.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

qt-ui/profile/diveprofileitem.cpp

@@ -782,6 +782,8 @@ void DiveGasPressureItem::paint(QPainter *painter, const QStyleOptionGraphicsIte
 		for (int i = 1, count = poly.count(); i < count; i++, entry++) {
 			if (entry->sac)
 				pen.setBrush(getSacColor(entry->sac, displayed_dive.sac));
+			else
+				pen.setBrush(MED_GRAY_HIGH_TRANS);
 			painter->setPen(pen);
 			painter->drawLine(poly[i - 1], poly[i]);
 		}