Fix missing deselection of single selected but not focused item

A generic multi-select wxListCtrl did not deselect a single selected
item that did not have focus when the user single-selected another
item.

This fixes a regression introduced in fedc80eee3 (Improve selection and
focus events generation in wxGenericLisCtrl, 2020-10-10).

Closes #24312.

src/generic/listctrl.cpp

@@ -2220,7 +2220,7 @@ void wxListMainWindow::HighlightOnly( size_t line, size_t oldLine )
                                : RefreshLine(oldLine); // refresh the old focus to remove it
     }
 
-    if ( selCount > 1 ) // multiple-selection only
+    if ( selCount >= 1 ) // multiple-selection only
     {
         // Deselecting many items at once will generate wxEVT_XXX_DESELECTED event
         // for each one of them. although this may be inefficient if the number of

tests/controls/listbasetest.cpp

@@ -273,6 +273,37 @@ void ListBaseTestCase::MultiSelect()
     CPPUNIT_ASSERT_EQUAL(1, focused.GetCount()); // because the focus changed from item 0 to anchor
     CPPUNIT_ASSERT_EQUAL(0, selected.GetCount()); // anchor is already in selection state
     CPPUNIT_ASSERT_EQUAL(2, deselected.GetCount()); // items 0 and 1 are deselected
+
+    focused.Clear();
+    selected.Clear();
+    deselected.Clear();
+
+    list->GetItemRect(3, pos);
+    point = list->ClientToScreen(pos.GetPosition()) + wxPoint(10, 10);
+
+    // select and deselect item 3 while leaving item 2 selected
+    for ( int i = 0; i < 2; ++i )
+    {
+        sim.MouseMove(point + wxPoint(i*10, 0));
+        wxYield();
+
+        sim.KeyDown(WXK_CONTROL);
+        sim.MouseClick();
+        sim.KeyUp(WXK_CONTROL);
+        wxYield();
+    }
+
+    // select only item 3
+    sim.MouseMove(point);
+    wxYield();
+
+    sim.MouseClick();
+    wxYield();
+
+    CPPUNIT_ASSERT_EQUAL(1, list->GetSelectedItemCount()); // item 3 is the only selected item
+    CPPUNIT_ASSERT_EQUAL(1, focused.GetCount()); // because the focus changed from anchor to item 3
+    CPPUNIT_ASSERT_EQUAL(2, selected.GetCount()); // item 3 was selected twice
+    CPPUNIT_ASSERT_EQUAL(2, deselected.GetCount()); // anchor and item 3 were each deselected once
 #endif // wxUSE_UIACTIONSIMULATOR
 }