Check that wxImageList::Create() is not called more than once

Or at least not until Destroy() is called.

include/wx/msw/imaglist.h

@@ -32,6 +32,7 @@ public:
   // from icons), and the initial size of the list.
   wxImageList(int width, int height, bool mask = true, int initialCount = 1)
   {
+    m_hImageList = 0;
     Create(width, height, mask, initialCount);
   }
   virtual ~wxImageList();

src/msw/imaglist.cpp

@@ -73,6 +73,8 @@ wxImageList::wxImageList()
 // Creates an image list
 bool wxImageList::Create(int width, int height, bool mask, int initial)
 {
+    wxASSERT_MSG( m_hImageList == NULL, "Recreating existing wxImageList?" );
+
     // Prevent from storing negative dimensions
     m_size = wxSize(wxMax(width, 0), wxMax(height, 0));
     UINT flags = 0;