win: avoid warning in StringFileWriter.SeekInvalid test

util/file/string_file_writer_test.cc

Index: util/file/string_file_writer_test.cc
diff --git a/util/file/string_file_writer_test.cc b/util/file/string_file_writer_test.cc
index ea26db3df6461756978a24a487144858dbbcf0d2..01b32369215bcbed4b46c19b3e78d01009f7680a 100644
--- a/util/file/string_file_writer_test.cc
+++ b/util/file/string_file_writer_test.cc
@@ -362,9 +362,9 @@ TEST(StringFileWriter, SeekInvalid) {
   EXPECT_EQ(0, writer.Seek(0, SEEK_CUR));
   EXPECT_TRUE(writer.string().empty());
 
-  const off_t kMaxOffset =
+  const off_t kMaxOffset = static_cast<off_t>(
       std::min(implicit_cast<uint64_t>(std::numeric_limits<off_t>::max()),
-               implicit_cast<uint64_t>(std::numeric_limits<size_t>::max()));
+               implicit_cast<uint64_t>(std::numeric_limits<size_t>::max())));
 
   EXPECT_EQ(kMaxOffset, writer.Seek(kMaxOffset, SEEK_SET));
   EXPECT_EQ(kMaxOffset, writer.Seek(0, SEEK_CUR));