Shut down fileWatcher more aggresively.

While I haven't been able to reproduce the crash, my theory is that
those that do are running into situations where wxWidgets defers
destructing the window.

Fixes https://gitlab.com/kicad/code/kicad/issues/8458

kicad/kicad_manager_frame.cpp

@@ -400,9 +400,7 @@ bool KICAD_MANAGER_FRAME::CloseProject( bool aSave )
         mgr.TriggerBackupIfNeeded( NULL_REPORTER::GetInstance() );
 
         if( aSave )
-        {
             mgr.SaveProject();
-        }
 
         m_active_project = false;
         mgr.UnloadProject( &Prj() );

kicad/project_tree_pane.cpp

@@ -32,7 +32,6 @@
 #include <wx/textdlg.h>
 
 #include <bitmaps.h>
-#include <common.h>
 #include <gestfich.h>
 #include <macros.h>
 #include <menus_helpers.h>
@@ -164,6 +163,12 @@ PROJECT_TREE_PANE::PROJECT_TREE_PANE( KICAD_MANAGER_FRAME* parent ) :
 
 
 PROJECT_TREE_PANE::~PROJECT_TREE_PANE()
+{
+    shutdownFileWatcher();
+}
+
+
+void PROJECT_TREE_PANE::shutdownFileWatcher()
 {
     if( m_watcher )
     {
@@ -1300,6 +1305,9 @@ void PROJECT_TREE_PANE::FileWatcherReset()
 
 void PROJECT_TREE_PANE::EmptyTreePrj()
 {
+    // Make sure we don't try to inspect the tree after we've deleted its items.
+    shutdownFileWatcher();
+
     m_TreeProject->DeleteAllItems();
 }
 

kicad/project_tree_pane.h

@@ -155,6 +155,12 @@ private:
      */
     void onIdle( wxIdleEvent &aEvent );
 
+    /**
+     * Shutdown the file watcher.  Used when closing to prevent post-free access into the project
+     * tree.  (Using the destructor doesn't work as wxWidgets defers destruction in some cases.)
+     */
+    void shutdownFileWatcher();
+
     /**
      * Function addItemToProjectTree
      * @brief  Add the file or directory aName to the project tree