ggml alloc: Fix for null dereference on alloc failure (ggerganov#5200)

* Fix for a null pointer dereference if a metal GGML buffer fails to be allocated

* Freeing the allocated buffers rather than the pointer in ggml-alloc.c

* Fixed the fix of the fix

ggml-alloc.c

@@ -791,7 +791,7 @@ static bool alloc_tensor_range(struct ggml_context * ctx,
         for (size_t i = 0; i < *n_buffers; i++) {
             ggml_backend_buffer_free(*buffers[i]);
         }
-        free(buffers);
+        free(*buffers);
         return false;
     }