Temporary dive + temporary site = crash

We always thought that a dive had a dive site
and that a dive really exists. but if we go
to add dive and then go to add dive site,
none of those exist yet and then we got a crash.

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

dive.h

@@ -624,6 +624,8 @@ static inline bool dive_site_has_gps_location(struct dive_site *ds)
 
 static inline int dive_has_gps_location(struct dive *dive)
 {
+	if (!dive)
+		return false;
 	return dive_site_has_gps_location(get_dive_site_by_uuid(dive->dive_site_uuid));
 }