Fix move assignment.

test/gtest-extra-test.cc

@@ -204,7 +204,7 @@ TEST(FileTest, MoveAssignmentClosesFile) {
   File f2("CMakeLists.txt", File::RDONLY);
   int old_fd = f2.descriptor();
   f2 = std::move(f);
-  EXPECT_TRUE(IsClosedInternal(old_fd));
+  EXPECT_CLOSED(old_fd);
 }
 
 File OpenFile(int &fd) {

test/gtest-extra.h

@@ -177,7 +177,8 @@ class File {
     other.fd_ = -1;
   }
 
-  File& operator=(File &&other) FMT_NOEXCEPT(true) {
+  File& operator=(File &&other) {
+    close();
     fd_ = other.fd_;
     other.fd_ = -1;
     return *this;