Set the columns in "Overview" mode to match the amount of pages if document is small

Summary:
FEATURE: 355283

The principle is simple. This patch enables overriding the default columns for Overview mode, if the document is small. For example, if document has 1 or 2 pages and the default columns in Okular settings is 3, Overview mode will enable 1 or 2 columns for better UX

Reviewers: #okular, rkflx, ngraham

Reviewed By: rkflx, ngraham

Subscribers: ltoscano, aacid, rkflx, ngraham

Tags: #okular

Differential Revision: https://phabricator.kde.org/D8385

ui/pageview.cpp

@@ -4181,6 +4181,9 @@ int PageView::viewColumns() const
     if (vm == Okular::Settings::EnumViewMode::Single) return 1;
     else if (vm == Okular::Settings::EnumViewMode::Facing ||
              vm == Okular::Settings::EnumViewMode::FacingFirstCentered) return 2;
+    else if (vm == Okular::Settings::EnumViewMode::Summary
+            && d->document->pages() < Okular::Settings::viewColumns() ) 
+            return d->document->pages();
     else return Okular::Settings::viewColumns();
 }