Clear is also expected to clear the text

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74174 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/osx/cocoa/combobox.mm

@@ -177,6 +177,7 @@ void wxNSComboBoxControl::Clear()
 {
     SendEvents(false);
     [m_comboBox removeAllItems];
+    [m_comboBox setStringValue:@""];
     SendEvents(true);
 }