处理grpc-opts为 {} 的情况

该字段仅影响sing-box内核，对mihomo无影响

backend/src/core/proxy-utils/index.js

@@ -415,6 +415,13 @@ function lastParse(proxy) {
         ) {
             delete proxy['reality-opts'];
         }
+        // 删除 grpc-opts: {}
+        if (
+            proxy['grpc-opts'] &&
+            Object.keys(proxy['grpc-opts']).length === 0
+        ) {
+            delete proxy['grpc-opts'];
+        }
         // 非 reality, 空 flow 没有意义
         if (!proxy['reality-opts'] && !proxy.flow) {
             delete proxy.flow;