KSPM: Ensure proper signalling when removing last selected

KSelectionProxyModel listens to two delegate objects for changes: the
source model of the proxy, and the selectionModel.  When a QModelIndex
which is selected gets removed, slots connected to signals for both
clients are executed.  Whichever slot is executed first updates the
KSelectionProxyModel, and when the other slot is executed it ignores the
already-handled event.

Until Qt 5.5. QItemSelectionModel required the model to be passed in its
constructor.  Prior to commit v5.9.0~21 (KSPM: Make the
setSelectionModel method public., 2015-03-08) the KSelectionProxyModel
required the selectionModel to be passed in its constructor.

Because the order of slot execution follows the order of signal slot
connection, the KSelectionProxyModel slot for handling deselection was
always executed first to process the removal.

Since Qt 5.5 and KItemModels 5.9.0, it is possible to set the model on
the QItemSelectionModel and the selectionModel on the
KSelectionProxyModel in a different order, meaning that the
(before/after) slots for handling removal of a row from the source model
is executed first.  When the before slot is executed the selectionModel
still has a selection, but by the time the after slot is executed the
selection has already been removed (because QItemSelectionModel updates
its selection on rowsAboutToBeRemoved).

Remove the check for the selection being empty in the after slot to
handle this case.

autotests/kselectionproxymodeltest.cpp

@@ -48,6 +48,7 @@ private Q_SLOTS:
   void columnCountShouldBeStable();
   void selectOnSourceReset();
   void selectionMapping();
+  void removeSelected();
 
 #if QT_VERSION >= QT_VERSION_CHECK(5, 5, 0)
   void selectionModelModelChange();
@@ -169,6 +170,27 @@ void KSelectionProxyModelTest::selectionModelModelChange()
   QCOMPARE(proxy.rowCount(), 1);
   QCOMPARE(proxy.index(0, 0).data().toString(), numbers.at(0));
 }
+
+void KSelectionProxyModelTest::removeSelected()
+{
+    QStringListModel strings(days);
+    QItemSelectionModel selectionModel;
+    KSelectionProxyModel proxy(&selectionModel);
+    proxy.setFilterBehavior(KSelectionProxyModel::ExactSelection);
+
+    proxy.setSourceModel(&strings);
+    selectionModel.setModel(&strings);
+
+    QSignalSpy beforeSpy(&proxy, SIGNAL(rowsAboutToBeRemoved(QModelIndex,int,int)));
+    QSignalSpy afterSpy(&proxy, SIGNAL(rowsRemoved(QModelIndex,int,int)));
+
+
+    selectionModel.select(strings.index(0, 0), QItemSelectionModel::Select);
+    strings.removeRow(0);
+
+    QCOMPARE(beforeSpy.count(), 1);
+    QCOMPARE(afterSpy.count(), 1);
+}
 #endif
 
 void KSelectionProxyModelTest::selectionMapping()

src/kselectionproxymodel.cpp

@@ -1291,7 +1291,7 @@ void KSelectionProxyModelPrivate::sourceRowsRemoved(const QModelIndex &parent, i
 
     Q_ASSERT(parent.isValid() ? parent.model() == q->sourceModel() : true);
 
-    if (!m_selectionModel || !m_selectionModel->hasSelection()) {
+    if (!m_selectionModel) {
         return;
     }