Extensions: suppress warnings when repository directories don't exist

Re-calculating statistics for outdated packages printed exceptions
whenever the repository directory didn't exist.

scripts/addons_core/bl_pkg/__init__.py

@@ -174,6 +174,7 @@ def repo_stats_calc():
     if bpy.app.background:
         return
 
+    import os
     package_count = 0
 
     for repo_item in bpy.context.preferences.extensions.repos:
@@ -184,7 +185,14 @@ def repo_stats_calc():
         if not repo_item.remote_url:
             continue
 
-        package_count += repo_stats_calc_outdated_for_repo_directory(repo_item.directory)
+        # If the directory is missing, ignore it.
+        # Otherwise users may be bothered with errors from unrelated repositories
+        # because calculating status currently runs after many actions.
+        repo_directory = repo_item.directory
+        if not os.path.isdir(repo_directory):
+            continue
+
+        package_count += repo_stats_calc_outdated_for_repo_directory(repo_directory)
 
     bpy.context.window_manager.extensions_updates = package_count