[simple-scan] Add missing enum value

[Robert Ancell <rancell src gnome org>]

commit 238c123caf429658f8108d4a319d98ee77f57233
Author: Robert Ancell <robert ancell canonical com>
Date:   Tue Sep 25 20:41:16 2018 +1200

    Add missing enum value

 src/page-view.vala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/page-view.vala b/src/page-view.vala
index 03fecfb..4adbc05 100644
--- a/src/page-view.vala
+++ b/src/page-view.vala
@@ -563,7 +563,7 @@ public class PageView
     private CropLocation get_crop_location (int x, int y)
     {
         if (!page.has_crop)
-            return 0;
+            return CropLocation.NONE;
 
         var cx = page.crop_x;
         var cy = page.crop_y;