[shotwell] export: Preserve GPS altitude

[Jens Georg <jensgeorg src gnome org>]

commit 905643301d70654a3963f9957256a8de839c21d8
Author: Jens Georg <mail jensge org>
Date:   Sat Aug 24 12:02:04 2019 +0200

    export: Preserve GPS altitude

 src/photos/PhotoMetadata.vala | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/src/photos/PhotoMetadata.vala b/src/photos/PhotoMetadata.vala
index 5a494835..bcd78fea 100644
--- a/src/photos/PhotoMetadata.vala
+++ b/src/photos/PhotoMetadata.vala
@@ -1183,9 +1183,11 @@ public class PhotoMetadata : MediaMetadata {
     }
 
     public void set_gps_coords(GpsCoords gps_coords) {
-        if (gps_coords.has_gps > 0)
-            exiv2.set_gps_info(gps_coords.longitude, gps_coords.latitude, 0.0);
-        else
+        if (gps_coords.has_gps > 0) {
+            var altitude = 0.0;
+            exiv2.get_gps_altitude(out altitude);
+            exiv2.set_gps_info(gps_coords.longitude, gps_coords.latitude, altitude);
+        } else
             exiv2.delete_gps_info();
     }