[packagechooser] Use all translations for no-package-selected

- If there is an item with id "" (empty), it is used as the
   "no-package-selected" placeholder text.
 - Existing code iterated over the abstract model and used the
   name and description at the time the model was set -- but
   by getting the name and description from the model, only
   a single string was obtained instead of the full range
   of translations.
 - Therefore, when arriving on the page, the "no-package-selected"
   information was displayed from the translation that was active
   when the model was set.

Instead, extend the non-abstract model so we can find the no-package-
selected item and pass that explicitly to the page.

FIXES #1241

src/modules/packagechooser/PackageChooserPage.cpp

@@ -129,26 +129,7 @@ void
 PackageChooserPage::setModel( QAbstractItemModel* model )
 {
     ui->products->setModel( model );
-
-    // Check if any of the items in the model is the "none" option.
-    // If so, copy its values into the introduction / none item.
-    for ( int r = 0; r < model->rowCount(); ++r )
-    {
-        auto index = model->index( r, 0 );
-        if ( index.isValid() )
-        {
-            QVariant v = model->data( index, PackageListModel::IdRole );
-            if ( v.isValid() && v.toString().isEmpty() )
-            {
-                m_introduction.name = model->data( index, PackageListModel::NameRole ).toString();
-                m_introduction.description = model->data( index, PackageListModel::DescriptionRole ).toString();
-                m_introduction.screenshot = model->data( index, PackageListModel::ScreenshotRole ).value< QPixmap >();
     currentChanged( QModelIndex() );
-                break;
-            }
-        }
-    }
-
     connect( ui->products->selectionModel(),
              &QItemSelectionModel::selectionChanged,
              this,
@@ -181,3 +162,11 @@ PackageChooserPage::selectedPackageIds() const
     }
     return ids;
 }
+
+void
+PackageChooserPage::setIntroduction( const CalamaresUtils::Locale::TranslatedString& name,
+                                     const CalamaresUtils::Locale::TranslatedString& description )
+{
+    m_introduction.name = name;
+    m_introduction.description = description;
+}

src/modules/packagechooser/PackageChooserPage.h

@@ -21,6 +21,8 @@
 
 #include "PackageModel.h"
 
+#include "locale/TranslatableConfiguration.h"
+
 #include <QAbstractItemModel>
 #include <QWidget>
 
@@ -37,6 +39,9 @@ public:
 
     void setModel( QAbstractItemModel* model );
 
+    /// @brief Sets the introductory (no-package-selected) texts
+    void setIntroduction( const CalamaresUtils::Locale::TranslatedString& name,
+                          const CalamaresUtils::Locale::TranslatedString& description );
     /// @brief Is anything selected?
     bool hasSelection() const;
     /** @brief Get the list of selected ids

src/modules/packagechooser/PackageChooserViewStep.cpp

@@ -283,4 +283,13 @@ PackageChooserViewStep::hookupModel()
     }
 
     m_widget->setModel( m_model );
+    for ( int i = 0; i < m_model->packageCount(); ++i )
+    {
+        const auto& package = m_model->packageData( i );
+        if ( package.id.isEmpty() )
+        {
+            m_widget->setIntroduction( package.name, package.description );
+            break;
+        }
+    }
 }

src/modules/packagechooser/PackageModel.h

@@ -80,6 +80,14 @@ struct PackageItem
      * A valid item has an untranslated name available.
      */
     bool isValid() const { return !name.isEmpty(); }
+
+    /** @brief Is this a (the) No-Package package?
+     *
+     * There should be at most one No-Package item in a collection
+     * of PackageItems. That one will be used to describe a
+     * "no package" situation.
+     */
+    bool isNonePackage() const { return id.isEmpty(); }
 };
 
 using PackageList = QVector< PackageItem >;
@@ -100,6 +108,11 @@ public:
     int rowCount( const QModelIndex& index ) const override;
     QVariant data( const QModelIndex& index, int role ) const override;
 
+    /// @brief Direct (non-abstract) access to package data
+    const PackageItem& packageData( int r ) const { return m_packages[ r ]; }
+    /// @brief Direct (non-abstract) count of package data
+    int packageCount() const { return m_packages.count(); }
+
     enum Roles : int
     {
         NameRole = Qt::DisplayRole,