Fix assert (in beginRemoveRows) when deselecting an empty child of a selected child in korganizer

After
   int proxyEndRemove = proxyStartRemove;
   proxyEndRemove += rc; was adding 0 (empty root)
and then --proxyEndRemove; was making us end up with proxyEndRemove < proxyStartRemove.

REVIEW: 129657

autotests/kselectionproxymodeltest.cpp

@@ -310,6 +310,13 @@ void KSelectionProxyModelTest::deselection_data()
             << 1
             << QStringList{"4"} << 5;
     ++testNumber;
+
+    QTest::newRow(QByteArray("test" + QByteArray::number(testNumber)).data())
+            << static_cast<int>(KSelectionProxyModel::ChildrenOfExactSelection)
+            << QStringList{"6", "7"} << 1
+            << 0
+            << QStringList{"7"} << 1;
+    ++testNumber;
 }
 
 void KSelectionProxyModelTest::deselection()
@@ -604,6 +611,13 @@ void KSelectionProxyModelTest::removeRows_data()
                   << 1
                   << QStringList{"9", "9"} << 2;
           ++testNumber;
+
+          QTest::newRow(QByteArray("test" + QByteArray::number(testNumber)).data())
+                  << static_cast<int>(kspm_mode) << connectSelectionModelFirst << false
+                  << QStringList{"6", "8", "11"} << 4
+                  << 0
+                  << QStringList{"8", "8"} << 4;
+          ++testNumber;
       }
   }
 

src/kselectionproxymodel.cpp

@@ -1176,7 +1176,7 @@ QPair<int, int> KSelectionProxyModelPrivate::beginRemoveRows(const QModelIndex &
     }
 
     --proxyEndRemove;
-    if (proxyEndRemove >= 0) {
+    if (proxyEndRemove >= proxyStartRemove) {
         return qMakePair(proxyStartRemove, proxyEndRemove);
     }
     return qMakePair(-1, -1);
@@ -1750,7 +1750,7 @@ void KSelectionProxyModelPrivate::removeSelectionFromProxy(const QItemSelection
     }
 
     --proxyEndRemove;
-    if (proxyEndRemove >= 0) {
+    if (proxyEndRemove >= proxyStartRemove) {
         q->beginRemoveRows(QModelIndex(), proxyStartRemove, proxyEndRemove);
 
         rootIt = m_rootIndexList.erase(rootRemoveStart, rootIt);
@@ -1953,7 +1953,7 @@ void KSelectionProxyModelPrivate::insertSelectionIntoProxy(const QItemSelection
 
             if (rowCount == 0) {
                 // Even if the newindex doesn't have any children to put into the model yet,
-                // We still need to make sure it's future children are inserted into the model.
+                // We still need to make sure its future children are inserted into the model.
                 m_rootIndexList.insert(rootListRow, newIndex);
                 if (!m_resetting || m_layoutChanging) {
                     emit q->rootIndexAdded(newIndex);