Fix storaged memory leak

storaged try to load user's proto even if it has been loaded before

https://partnerissuetracker.corp.google.com/u/2/issues/118719575

Change-Id: Ia7575cdc60e82b028c6db9a29ae80e31e02268b1
diff --git a/storaged/storaged.cpp b/storaged/storaged.cpp
index 77c6167..089390a 100644
--- a/storaged/storaged.cpp
+++ b/storaged/storaged.cpp
@@ -164,8 +164,10 @@
 }
 
 void storaged_t::add_user_ce(userid_t user_id) {
-    load_proto(user_id);
-    proto_loaded[user_id] = true;
+    if (!proto_loaded[user_id]) {
+        load_proto(user_id);
+        proto_loaded[user_id] = true;
+    }
 }
 
 void storaged_t::remove_user_ce(userid_t user_id) {