improve mixpanel usage statistics (#2238)

Other changes:
- Always display first start dialog if privacy options are unset (e.g. if the user closed GPT4All without selecting them)
- LocalDocs scanQueue is now always deferred
- Fix a potential crash in magic_match
- LocalDocs indexing is now started after the first start dialog is dismissed so usage stats are included

Signed-off-by: Jared Van Bortel <jared@nomic.ai>

gpt4all-backend/llmodel_c.cpp

@@ -40,11 +40,6 @@ llmodel_model llmodel_model_create2(const char *model_path, const char *build_va
         return nullptr;
     }
 
-    if (!llModel) {
-        llmodel_set_error(error, "Model format not supported (no matching implementation found)");
-        return nullptr;
-    }
-
     auto wrapper = new LLModelWrapper;
     wrapper->llModel = llModel;
     return wrapper;