Expose default ('--_--') locale in proto format.

Bug: b/243145989
Test: Dump_test
Change-Id: Ie56aabb0f9b4b923d560470db7b426ab6ee34bd2
diff --git a/tools/aapt2/dump/DumpManifest.cpp b/tools/aapt2/dump/DumpManifest.cpp
index b3165d3..2a5ad96 100644
--- a/tools/aapt2/dump/DumpManifest.cpp
+++ b/tools/aapt2/dump/DumpManifest.cpp
@@ -2845,7 +2845,9 @@
   supports_screen_->ToProtoScreens(out_badging, target_sdk_);
 
   for (auto& config : locales_) {
-    if (!config.first.empty()) {
+    if (config.first.empty()) {
+      out_badging->add_locales("--_--");
+    } else {
       out_badging->add_locales(config.first);
     }
   }