Fix zero initialization of the other fields.

main.cpp

@@ -551,7 +551,7 @@ bool llama_eval(
     };
 
     struct ggml_context * ctx0 = ggml_init(params);
-    struct ggml_cgraph gf;
+    ggml_cgraph gf = {};
     gf.n_threads = n_threads;
 
     struct ggml_tensor * embd = ggml_new_tensor_1d(ctx0, GGML_TYPE_I32, N);