Recognize "_" as alphanumeric key in wxGenericTreeCtrl find item code.

Items can have underscores in their names too, not just letters and digits.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72635 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/treectlg.cpp

@@ -3305,7 +3305,8 @@ void wxGenericTreeCtrl::OnChar( wxKeyEvent &event )
             if ( !event.HasModifiers() &&
                  ((keyCode >= '0' && keyCode <= '9') ||
                   (keyCode >= 'a' && keyCode <= 'z') ||
-                  (keyCode >= 'A' && keyCode <= 'Z' )))
+                  (keyCode >= 'A' && keyCode <= 'Z') ||
+                  (keyCode == '_')))
             {
                 // find the next item starting with the given prefix
                 wxChar ch = (wxChar)keyCode;