Initialize these to nullptr to prevent double deletion when a model fails to load.

gpt4all-backend/gptj.cpp

@@ -833,6 +833,7 @@ struct GPTJPrivate {
 GPTJ::GPTJ()
     : d_ptr(new GPTJPrivate) {
     d_ptr->model = new gptj_model;
+    d_ptr->model->ctx = nullptr;
     d_ptr->modelLoaded = false;
 }
 

gpt4all-backend/mpt.cpp

@@ -757,6 +757,7 @@ struct MPTPrivate {
 MPT::MPT()
     : d_ptr(new MPTPrivate) {
     d_ptr->model = new mpt_model;
+    d_ptr->model->ctx = nullptr;
     d_ptr->modelLoaded = false;
 }
 

gpt4all-backend/replit.cpp

@@ -884,6 +884,7 @@ Replit::Replit()
     : d_ptr(new ReplitPrivate) {
 
     d_ptr->model = new replit_model;
+    d_ptr->model->ctx = nullptr;
     d_ptr->modelLoaded = false;
 }