AAPT2: better error handling for daemon mode

Test: manual
Change-Id: Ia1997800ad94f386dbbb4195011395ecee1ba91f
diff --git a/tools/aapt2/Main.cpp b/tools/aapt2/Main.cpp
index e4ca7a4..82977cb 100644
--- a/tools/aapt2/Main.cpp
+++ b/tools/aapt2/Main.cpp
@@ -101,10 +101,12 @@
 
     std::vector<StringPiece> args;
     args.insert(args.end(), token_iter, tokenizer.end());
-    ExecuteCommand(command, args, diagnostics);
-    std::cout << "Done" << std::endl;
+    int ret = ExecuteCommand(command, args, diagnostics);
+    if (ret != 0) {
+      std::cerr << "Error" << std::endl;
+    }
+    std::cerr << "Done" << std::endl;
   }
-
   std::cout << "Exiting daemon" << std::endl;
 }