Remove close when fd == -1. (facebook#12732)

Summary:
Its polluting my valgrind runs:
==3733139== Warning: invalid file descriptor -1 in syscall close()
==3733139== Warning: invalid file descriptor -1 in syscall close()
==3733139== Warning: invalid file descriptor -1 in syscall close()

Pull Request resolved: facebook#12732

Reviewed By: ltamasi

Differential Revision: D58170009

Pulled By: ajkr

fbshipit-source-id: 1fc6944c2667641996676a75aa3e91984070ba49

env/io_posix.cc

@@ -457,7 +457,6 @@ Status PosixHelper::GetLogicalBlockSizeOfDirectory(const std::string& directory,
                                                    size_t* size) {
   int fd = open(directory.c_str(), O_DIRECTORY | O_RDONLY);
   if (fd == -1) {
-    close(fd);
     return Status::IOError("Cannot open directory " + directory);
   }
   *size = PosixHelper::GetLogicalBlockSizeOfFd(fd);