Fix initial state of radio toolbar tools in wxGTK.

The last radio group item was initially checked under wxGTK instead of the
first one, as under the other platforms. Fix this by correcting the check for
the first radio group item which was inversed in wxToolBar::DoInsertTool().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70510 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk/toolbar.cpp

@@ -502,7 +502,7 @@ bool wxToolBar::DoInsertTool(size_t pos, wxToolBarToolBase *toolBase)
                     break;
                 case wxITEM_RADIO:
                     radioGroup = GetRadioGroup(pos);
-                    if (radioGroup)
+                    if (!radioGroup)
                     {
                         // this is the first button in the radio button group,
                         // it will be toggled automatically by GTK so bring the