Do not try retrieve an unconfigured core content type in Config GUI

Previous behavior was resulting in a null reference error. As key for
the core content/search type was not present in current config

Fallback to using default config for unconfigured core content type
instead

See #165 for details

src/khoj/interface/desktop/main_window.py

@@ -58,9 +58,9 @@ def __init__(self, config_file: Path):
         # Add Settings Panels for each Search Type to Configure Window Layout
         self.search_settings_panels = []
         for search_type in SearchType:
-            current_content_config = self.current_config["content-type"][search_type] or self.get_default_config(
-                search_type=search_type
-            )
+            current_content_config = self.current_config["content-type"].get(
+                search_type, None
+            ) or self.get_default_config(search_type=search_type)
             self.search_settings_panels += [self.add_settings_panel(current_content_config, search_type)]
 
         # Add Conversation Processor Panel to Configure Screen