Fix app list model filter ordering and reset handling

ApplicationListSearchModel: beginFilterChange() was called after
mutating m_categoryFilter, inverting the documented before/after
contract. Also add null checks for sourceModel() and
favouritesModel() in filterAcceptsRow.

CategoryPanel: add onModelReset to repopulate the category list
when the underlying model is fully reloaded, not just on individual
row insertions and removals.

containments/homescreens/folio/applicationlistmodel.cpp

@@ -250,9 +250,9 @@ void ApplicationListSearchModel::setCategoryFilter(const QString &filter)
 {
     if (m_categoryFilter == filter)
         return;
+    beginFilterChange();
     m_categoryFilter = filter;
     Q_EMIT categoryFilterChanged();
-    beginFilterChange();
     endFilterChange(QSortFilterProxyModel::Direction::Rows);
 }
 
@@ -265,13 +265,21 @@ bool ApplicationListSearchModel::filterAcceptsRow(int sourceRow, const QModelInd
         return true;
 
     auto *src = static_cast<ApplicationListModel *>(sourceModel());
+    if (!src)
+        return false;
     const QModelIndex idx = src->index(sourceRow, 0, sourceParent);
     auto *del = src->data(idx, ApplicationListModel::DelegateRole).value<FolioDelegate *>();
     if (!del || !del->application())
         return false;
 
-    if (m_categoryFilter == QLatin1String("__favorites__"))
+    if (m_categoryFilter == QLatin1String("__favorites__")) {
-        return m_homeScreen->favouritesModel()->containsApplication(del->application()->storageId());
+        if (!m_homeScreen)
+            return false;
+        auto *favModel = m_homeScreen->favouritesModel();
+        if (!favModel)
+            return false;
+        return favModel->containsApplication(del->application()->storageId());
+    }
 
     // Match both the canonical name and any raw aliases it absorbs.
     const QStringList &cats = del->application()->categories();

containments/homescreens/folio/qml/CategoryPanel.qml

@@ -80,6 +80,7 @@ Rectangle {
         target: folio.ApplicationListModel
         function onRowsInserted() { root.populate() }
         function onRowsRemoved()  { root.populate() }
+        function onModelReset()   { root.populate() }
     }
 
     // ---------- tile list ----------