Don't keep all the split dives invisibly selected

While the visual state didn't show it, our internal tracking of the
selected state was copied causing all kinds of unexpected behavior. With
this commit we get this right.

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

dive.c

@@ -2860,6 +2860,11 @@ static int split_dive_at(struct dive *dive, int a, int b)
 	d1 = create_new_copy(dive);
 	d2 = create_new_copy(dive);
 
+	/* now unselect the first first segment so we don't keep all
+	 * dives selected by mistake. But do keep the second one selected
+	 * so the algorithm keeps splitting the dive further */
+	d1->selected = false;
+
 	dc1 = &d1->dc;
 	dc2 = &d2->dc;
 	/*