Fixed X11 related crash that occured when GraphicsWindow::setCursor was called right after viewer.realize();

The fix was to simply move the setting of the thread that has done the makeCurrent to right before the makeCurrent()
rather than right after.

src/osg/GraphicsContext.cpp

@@ -579,12 +579,12 @@ void GraphicsContext::close(bool callCloseImplementation)
 
 bool GraphicsContext::makeCurrent()
 {
+    _threadOfLastMakeCurrent = OpenThreads::Thread::CurrentThread();
+
     bool result = makeCurrentImplementation();
     
     if (result)
     {
-        _threadOfLastMakeCurrent = OpenThreads::Thread::CurrentThread();
-
         // initialize extension process, not only initializes on first
         // call, will be a non-op on subsequent calls.        
         getState()->initializeExtensionProcs();