llama : add option to override model tensor buffers (llama/11397)

* llama : add option to override tensor buffers

* ggml : fix possible underflow in ggml_nbytes

ggml/src/ggml.c

@@ -1159,6 +1159,12 @@ int64_t ggml_nrows(const struct ggml_tensor * tensor) {
 }
 
 size_t ggml_nbytes(const struct ggml_tensor * tensor) {
+    for (int i = 0; i < GGML_MAX_DIMS; ++i) {
+        if (tensor->ne[i] <= 0) {
+            return 0;
+        }
+    }
+
     size_t nbytes;
     const size_t blck_size = ggml_blck_size(tensor->type);
     if (blck_size == 1) {