Fix fd leak when using direct IOs

Summary:
We should close the fd, before overriding it. This bug was
introduced by f89caa127b
Closes https://github.com/facebook/rocksdb/pull/1553

Differential Revision: D4214101

Pulled By: siying

fbshipit-source-id: 0d65de0

util/env_posix.cc

@@ -157,6 +157,7 @@ class PosixEnv : public Env {
       *result = nullptr;
       return IOError(fname, errno);
     } else if (options.use_direct_reads && !options.use_mmap_writes) {
+      fclose(f);
 #ifdef OS_MACOSX
       int flags = O_RDONLY;
 #else
@@ -215,6 +216,7 @@ class PosixEnv : public Env {
       }
       close(fd);
     } else if (options.use_direct_reads) {
+      close(fd);
 #ifdef OS_MACOSX
       int flags = O_RDONLY;
 #else
@@ -269,6 +271,7 @@ class PosixEnv : public Env {
       if (options.use_mmap_writes && !forceMmapOff) {
         result->reset(new PosixMmapFile(fname, fd, page_size_, options));
       } else if (options.use_direct_writes) {
+        close(fd);
 #ifdef OS_MACOSX
         int flags = O_WRONLY | O_APPEND | O_TRUNC | O_CREAT;
 #else