UI restructure: fix get_divenr to do the right thing on a copy of a dive

We should not care if the dive has the same address in memory. We care if
it is the same dive (by using the unique ID).

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

divelist.c

@@ -339,7 +339,7 @@ int get_divenr(struct dive *dive)
 	int i;
 	struct dive *d;
 	for_each_dive(i, d) {
-		if (d == dive)
+		if (d->id == dive->id) // don't compare pointers, we could be passing in a copy of the dive
 			return i;
 	}
 	return -1;