Replace wxComboBox::IsEmpty() with Is{List,Text}Empty().

IsEmpty() didn't exist in all ports (notably not wxMSW) and its meaning was
unclear anyhow, so remove it even from the ports where it did exist and add
clear Is{List,Text}Empty() replacements instead.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68808 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/combobox.h

@@ -36,7 +36,13 @@ public:
         wxItemContainer::Clear();
     }
 
-    bool IsEmpty() const { return wxItemContainer::IsEmpty(); }
+    // IsEmpty() is ambiguous because we inherit it from both wxItemContainer
+    // and wxTextEntry, and even if defined it here to help the compiler with
+    // choosing one of them, it would still be confusing for the human users of
+    // this class. So instead define the clearly named methods below and leave
+    // IsEmpty() ambiguous to trigger a compilation error if it's used.
+    bool IsListEmpty() const { return wxItemContainer::IsEmpty(); }
+    bool IsTextEmpty() const { return wxTextEntry::IsEmpty(); }
 
     // also bring in GetSelection() versions of both base classes in scope
     //