[shotwell] map: Fix logic for show_position_markers

[Jens Georg <jensgeorg src gnome org>]

commit e84942c7a1d4e298a55455e5d0bcfc7e59f312e6
Author: Andreas Brauchli <a brauchli elementarea net>
Date:   Thu Jun 23 09:52:14 2016 +0200

    map: Fix logic for show_position_markers

 src/MapWidget.vala | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)
---
diff --git a/src/MapWidget.vala b/src/MapWidget.vala
index de936d23..cbc82a6f 100644
--- a/src/MapWidget.vala
+++ b/src/MapWidget.vala
@@ -124,6 +124,12 @@ private class MarkerGroupRaster : Object {
     private Champlain.View map_view;
     private Champlain.MarkerLayer marker_layer;
 
+    public bool is_empty {
+        get {
+            return position_markers.is_empty;
+        }
+    }
+
     // position_markers_tree is a two-dimensional tree for grouping position
     // markers indexed by x (outer tree) and y (inner tree) raster coordinates.
     // It maps coordinates to the PositionMarker (DataViewMarker or MarkerGroup)
@@ -163,10 +169,6 @@ private class MarkerGroupRaster : Object {
         return m;
     }
 
-    public bool has_markers() {
-        return !position_markers.is_empty;
-    }
-
     public void rasterize_marker(PositionMarker position_marker, bool already_on_map=false) {
         var data_view_position_marker = position_marker as DataViewPositionMarker;
         var champlain_marker = position_marker.champlain_marker;
@@ -331,7 +333,7 @@ private class MapWidget : Gtk.Bin {
     }
 
     public void show_position_markers() {
-        if (!marker_group_raster.has_markers()) {
+        if (!marker_group_raster.is_empty) {
             if (map_view.get_zoom_level() < DEFAULT_ZOOM_LEVEL) {
                 map_view.set_zoom_level(DEFAULT_ZOOM_LEVEL);
             }