[srp-server] avoid re-accessing committed SRP updates (openthread#6785)

We should remove the UpdateMetadata before committing the SRP update
to ensure that the same UpdateMetadata (and the Host object) can never
be touched again.

src/core/net/srp_server.cpp

@@ -298,9 +298,8 @@ void Server::HandleServiceUpdateResult(ServiceUpdateId aId, Error aError)
 
 void Server::HandleServiceUpdateResult(UpdateMetadata *aUpdate, Error aError)
 {
-    CommitSrpUpdate(aError, aUpdate->GetDnsHeader(), aUpdate->GetHost(), aUpdate->GetMessageInfo());
-
     IgnoreError(mOutstandingUpdates.Remove(*aUpdate));
+    CommitSrpUpdate(aError, aUpdate->GetDnsHeader(), aUpdate->GetHost(), aUpdate->GetMessageInfo());
     aUpdate->Free();
 
     if (mOutstandingUpdates.IsEmpty())