No changes, just use symbolic NO_IMAGE constant instead of -1 or wxNOT_FOUND.

Existing declarations used -1 in several places to indicate the absence of the
image which wasn't especially clear and was also inconsistent with other
places that used wxNOT_FOUND which didn't make much sense in this context.

Add a new symbolic constant NO_IMAGE in wxWithImages and use it in the classes
deriving from it. This still doesn't help with wx{Tree,List}Ctrl but improves
clarity for the other classes.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68810 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/withimages.h

@@ -21,6 +21,11 @@
 class WXDLLIMPEXP_CORE wxWithImages
 {
 public:
+    enum
+    {
+        NO_IMAGE = -1
+    };
+
     wxWithImages()
     {
         m_imageList = NULL;
@@ -55,13 +60,13 @@ protected:
 
     // Return the image with the given index from the image list.
     //
-    // If there is no image list or if index == -1 (which traditionally means
-    // that no image should be used for the given item), silently returns
+    // If there is no image list or if index == NO_IMAGE, silently returns
     // wxNullIcon.
     wxIcon GetImage(int iconIndex) const
     {
-        return m_imageList && iconIndex != -1 ? m_imageList->GetIcon(iconIndex)
-                                              : wxNullIcon;
+        return m_imageList && iconIndex != NO_IMAGE
+                    ? m_imageList->GetIcon(iconIndex)
+                    : wxNullIcon;
     }
 
 private: