Fix ijar failing on empty jars.

The problem happens when all the files are filtered out. In such case a dummy file is created, but not accounted for in the size estimation.
Fixes bazelbuild#10162

third_party/ijar/ijar.cc

@@ -54,6 +54,8 @@ const char *TARGET_LABEL_KEY = "Target-Label: ";
 const size_t TARGET_LABEL_KEY_LENGTH = strlen(TARGET_LABEL_KEY);
 const char *INJECTING_RULE_KIND_KEY = "Injecting-Rule-Kind: ";
 const size_t INJECTING_RULE_KIND_KEY_LENGTH = strlen(INJECTING_RULE_KIND_KEY);
+const char *DUMMY_FILE = "dummy";
+const size_t DUMMY_PATH_LENGTH = strlen(DUMMY_FILE);
 
 class JarExtractorProcessor : public ZipExtractorProcessor {
  public:
@@ -369,7 +371,7 @@ static void OpenFilesAndProcessJar(const char *file_out, const char *file_in,
     abort();
   }
   u8 output_length =
-      in->CalculateOutputLength() +
+      std::max(in->CalculateOutputLength(), 103ull + DUMMY_PATH_LENGTH) +
       EstimateManifestOutputSize(target_label, injecting_rule_kind);
   std::unique_ptr<ZipBuilder> out(ZipBuilder::Create(file_out, output_length));
   if (out == NULL) {
@@ -388,7 +390,7 @@ static void OpenFilesAndProcessJar(const char *file_out, const char *file_in,
 
   // Add dummy file, since javac doesn't like truly empty jars.
   if (out->GetNumberFiles() == 0) {
-    out->WriteEmptyFile("dummy");
+    out->WriteEmptyFile(DUMMY_FILE);
   }
   // Finish writing the output file
   if (out->Finish() < 0) {