Synchronously release lock in FileSystemSyncAccessHandle's close()

Fixes whatwg#83.

index.bs

@@ -1238,14 +1238,19 @@ The <dfn method for=FileSystemSyncAccessHandle>flush()</dfn> method steps are:
 
 <div class="note domintro">
   : |handle| . {{FileSystemSyncAccessHandle/close()}}
-  :: Closes the access handle. This disables any further operations on it and
+  :: Closes the access handle or no-ops if the access handle is already closed.
+     This disables any further operations on it and
      [=file entry/lock/release|releases the lock=] on the
      [=FileSystemHandle/entry=] associated with |handle|.
 </div>
 
 <div algorithm>
-The <dfn method for=FileSystemSyncAccessHandle>close()</dfn> method steps are
-to set [=this=].[=[[state]]=] to "`closed`".
+The <dfn method for=FileSystemSyncAccessHandle>close()</dfn> method steps are:
+
+1. If [=this=]'s [=[[state]]=] is "`closed`", return.
+1. Set [=this=]'s [=[[state]]=] to "`closed`".
+1. [=file entry/lock/release|Release the lock=] on
+   [=this=]'s [=FileSystemSyncAccessHandle/[[file]]=].
 
 Note: This method does not guarantee that all file modifications will be
 immediately reflected in the underlying storage device. Call the