lib_tree.cpp: Fix a lot of wxWidgets alerts on Windows.

On Windows calling m_adapter->RefreshTree() to refresh the tree does not work fine.
Just calling Refresh() is enough.

common/widgets/lib_tree.cpp

@@ -216,7 +216,14 @@ void LIB_TREE::Regenerate( bool aKeepState )
 
 void LIB_TREE::RefreshLibTree()
 {
+    // m_adapter->RefreshTree() does not work fine on Windows.
+    // It creates a lot of wxWidgets alerts.
+    // calling Refresh of the wxPanel is enough
+#ifdef _WINDOWS_
+    Refresh();
+#else
     m_adapter->RefreshTree();
+#endif
 }