[simple-scan] Display an error, when no documents found in the feeder during start scanning

[Bartosz <bkosiorek src gnome org>]

commit ede0720824d087168cab0f1a5954014c58bb34d4
Author: Bartosz Kosiorek <gang65 poczta onet pl>
Date:   Fri Aug 21 20:59:54 2020 +0200

    Display an error, when no documents found in the feeder during start scanning
    
    Fixes: #195

 src/scanner.vala | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/src/scanner.vala b/src/scanner.vala
index 5b704e1d..237e1eb9 100644
--- a/src/scanner.vala
+++ b/src/scanner.vala
@@ -1426,6 +1426,10 @@ public class Scanner : Object
         if (status == Sane.Status.NO_DOCS)
         {
             do_complete_document ();
+            if (page_number == 0)
+                fail_scan (status,
+                    /* Error displayed when no documents at the start of scanning */
+                    _("Document feeder empty"));
             return;
         }