add constructor to initialize server_context::batch, preventing destructor's call to llama_batch_free from causing an invalid free()

Author: aumfer

tools/server/server.cpp

@@ -1884,6 +1884,8 @@ struct server_context {
 
     common_chat_templates_ptr chat_templates;
 
+    server_context() : batch({}) {
+    }
     ~server_context() {
         mtmd_free(mctx);