Unselect and freeze before starting reset

In some cases, the BeforeReset() will cause an iteration over the tree
elements.  If we have deleted an element before doing this, we risk a
corruption/crash.

Fixes https://gitlab.com/kicad/code/kicad/issues/6192

(cherry picked from commit 3bd080b64e)

common/lib_tree_model_adapter.cpp

@@ -144,7 +144,6 @@ void LIB_TREE_MODEL_ADAPTER::UpdateSearchString( wxString const& aSearch )
         // not return invalid data to the UI, since this invalid data can cause crashes.
         // This is different than the update locker, which locks the UI aspects only.
         wxWindowUpdateLocker updateLock( m_widget );
-        BeforeReset();
 
         // Even with the updateLock, wxWidgets sometimes ties its knickers in
         // a knot when trying to run a wxdataview_selection_changed_callback()
@@ -152,6 +151,7 @@ void LIB_TREE_MODEL_ADAPTER::UpdateSearchString( wxString const& aSearch )
         // https://bugs.launchpad.net/kicad/+bug/1756255
         m_widget->UnselectAll();
         Freeze();
+        BeforeReset();
 
         m_tree.ResetScore();