Fix progress calculation, don't display progress for documents

under five pages long.

Current page is 0-based so progress was being displayed off by
one - a document was never fully read/last page.

Either way, progress display can be confusing for short documents,
but it's not really necessary either, so only show progress for
longer documents (5 pages or more).

usr/lib/thingy/thingy.py

@@ -268,15 +268,16 @@ def add_document_to_library(self, uri, app_id, mark_as_favorite):
         progress_tracked = False
         if num_pages is not None and current_page is not None:
             num_pages = int(num_pages)
-            current_page = int(current_page)
-            if current_page > 0:
-                progress = float(current_page) / float(num_pages)
-                bar = Gtk.ProgressBar()
-                bar.set_fraction(progress)
-                bar.set_margin_start(50)
-                bar.set_margin_end(50)
-                box.pack_end(bar, False, False, 0)
-                progress_tracked = True
+            if num_pages > 4:
+                current_page = int(current_page)
+                if current_page > 0:
+                    progress = float(current_page) / float(num_pages - 1)
+                    bar = Gtk.ProgressBar()
+                    bar.set_fraction(progress)
+                    bar.set_margin_start(50)
+                    bar.set_margin_end(50)
+                    box.pack_end(bar, False, False, 0)
+                    progress_tracked = True
 
         if not progress_tracked:
             box.pack_end(Gtk.Label(), False, False, 0)