[simple-scan] Change the size of the paper to avoid visual glitches

[Bartosz <bkosiorek src gnome org>]

commit 8b68ad8a8cab3021dbbbccc793c78e74cf1aa440
Author: Bartosz Kosiorek <gang65 poczta onet pl>
Date:   Tue May 26 00:33:26 2020 +0200

    Change the size of the paper to avoid visual glitches
    
    Fixes: #179

 src/simple-scan.vala | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/simple-scan.vala b/src/simple-scan.vala
index 64562aa..450ac86 100644
--- a/src/simple-scan.vala
+++ b/src/simple-scan.vala
@@ -1817,7 +1817,8 @@ public class SimpleScan : Gtk.Application
         debug ("Requesting scan at %d dpi from device '%s'", options.dpi, device);
 
         if (!scanner.is_scanning ())
-            append_page (options.paper_width, options.paper_height, options.dpi);
+            // We need to add +1 to avoid visual glitches, fixes: #179
+            append_page (options.paper_width + 1, options.paper_height + 1, options.dpi + 1);
 
         scanner.scan (device, options);
     }