Don't write files with no fixes.

llvm-svn: 217163
diff --git a/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp b/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp
index 6048217..289b4f8 100644
--- a/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp
+++ b/clang-tools-extra/clang-tidy/tool/ClangTidyMain.cpp
@@ -190,7 +190,7 @@
       OptionsParser.getSourcePathList(), &Errors);
   clang::tidy::handleErrors(Errors, Fix);
 
-  if (!ExportFixes.empty()) {
+  if (!ExportFixes.empty() && !Errors.empty()) {
     std::error_code EC;
     llvm::raw_fd_ostream OS(ExportFixes, EC, llvm::sys::fs::F_None);
     if (EC) {