Fixed a crash related to file transfers

file/local_server/LocalFileTransfer.cpp

@@ -22,9 +22,16 @@ Buffer* transfer::allocate_buffer(size_t size) {
     return buffer;
 }
 
-void transfer::free_buffer(Buffer* buffer) {
-    buffer->~Buffer();
-    free(buffer);
+Buffer* transfer::ref_buffer(Buffer *buffer) {
+    buffer->ref_count++;
+    return buffer;
+}
+
+void transfer::deref_buffer(Buffer *buffer) {
+    if(--buffer->ref_count == 0) {
+        buffer->~Buffer();
+        free(buffer);
+    }
 }
 
 FileClient::~FileClient() {