AAPT2: Make sure to fail when XML linking fails

Bug: 64367402
Test: manual
Change-Id: I3082887f5e449d8d0dac2aad93a834eb346008ba
diff --git a/tools/aapt2/cmd/Link.cpp b/tools/aapt2/cmd/Link.cpp
index e6bf3a6..5ad0cdd 100644
--- a/tools/aapt2/cmd/Link.cpp
+++ b/tools/aapt2/cmd/Link.cpp
@@ -574,6 +574,11 @@
         if (file_op.xml_to_flatten) {
           std::vector<std::unique_ptr<xml::XmlResource>> versioned_docs =
               LinkAndVersionXmlFile(table, &file_op);
+          if (versioned_docs.empty()) {
+            error = true;
+            continue;
+          }
+
           for (std::unique_ptr<xml::XmlResource>& doc : versioned_docs) {
             std::string dst_path = file_op.dst_path;
             if (doc->file.config != file_op.config) {