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

interface/wx/combobox.h

@@ -224,6 +224,39 @@ public:
     */
     virtual long GetInsertionPoint() const;
 
+    /**
+        IsEmpty() is not available in this class.
+
+        This method is documented here only to notice that it can't be used
+        with this class because of the ambiguity between the methods with the
+        same name inherited from wxItemContainer and wxTextEntry base classes.
+
+        Because of this, any attempt to call it results in a compilation error
+        and you should use either IsListEmpty() or IsTextEmpty() depending on
+        what exactly do you want to test.
+     */
+    bool IsEmpty() const;
+
+    /**
+        Returns true if the list of combobox choices is empty.
+
+        Use this method instead of (not available in this class) IsEmpty() to
+        test if the list of items is empty.
+
+        @since 2.9.3
+     */
+    bool IsListEmpty() const;
+
+    /**
+        Returns true if the text of the combobox is empty.
+
+        Use this method instead of (not available in this class) IsEmpty() to
+        test if the text currently entered into the combobox is empty.
+
+        @since 2.9.3
+     */
+    bool IsTextEmpty() const;
+
     /**
         Same as wxTextEntry::SetSelection().