Update ggml/src/gguf.cpp : Defined virtual keyword for destructor of gguf_writer_base (llama/25867)

Without a virtual destructor, deleting a derived object through a
base-class pointer only invokes the base destructor, skipping the
derived one.

ggml/src/gguf.cpp

@@ -1424,7 +1424,7 @@ void gguf_set_tensor_data(struct gguf_context * ctx, const char * name, const vo
 struct gguf_writer_base {
     size_t written_bytes {0u};
 
-    ~gguf_writer_base(void) = default;
+    virtual ~gguf_writer_base(void) = default;
 
     // we bet on devirtualization
     virtual void write(int8_t val) = 0;