Reset the wxDataViewItem being edited once it's not edited any more

No real changes, just some cleanup to ensure that the item being edited stored
in wxDataViewRendererBase never refers to an item which is not, actually,
being edited any longer.

include/wx/dvrenderers.h

@@ -202,7 +202,7 @@ protected:
     wxString                m_variantType;
     wxDataViewColumn       *m_owner;
     wxWeakRef<wxWindow>     m_editorCtrl;
-    wxDataViewItem          m_item; // for m_editorCtrl
+    wxDataViewItem          m_item; // Item being currently edited, if valid.
 
     // internal utility, may be used anywhere the window associated with the
     // renderer is required

src/common/datavcmn.cpp

@@ -681,8 +681,6 @@ bool wxDataViewRendererBase::StartEditing( const wxDataViewItem &item, wxRect la
     if( !start_event.IsAllowed() )
         return false;
 
-    m_item = item; // remember for later
-
     unsigned int col = GetOwner()->GetModelColumn();
     const wxVariant& value = CheckedGetValue(dv_ctrl->GetModel(), item, col);
 
@@ -708,6 +706,9 @@ bool wxDataViewRendererBase::StartEditing( const wxDataViewItem &item, wxRect la
 
 void wxDataViewRendererBase::NotifyEditingStarted(const wxDataViewItem& item)
 {
+    // Remember the item being edited for use in FinishEditing() later.
+    m_item = item;
+
     wxDataViewColumn* const column = GetOwner();
     wxDataViewCtrl* const dv_ctrl = column->GetOwner();
 
@@ -778,13 +779,16 @@ bool wxDataViewRendererBase::FinishEditing()
     event.SetEventObject( dv_ctrl );
     dv_ctrl->GetEventHandler()->ProcessEvent( event );
 
+    bool accepted = false;
     if ( isValid && event.IsAllowed() )
     {
         dv_ctrl->GetModel()->ChangeValue(value, m_item, col);
-        return true;
+        accepted = true;
     }
 
-    return false;
+    m_item = wxDataViewItem();
+
+    return accepted;
 }
 
 wxVariant