fusefrontend: unregister from openfiletable before closing the fd

Closing the fd means the inode number may be reused immediately
by a new file, so we have to get the old fileID out of the table
beforehand!

Hopefully fixes https://github.com/rfjakob/gocryptfs/issues/363

internal/fusefrontend/file.go

@@ -401,11 +401,10 @@ func (f *File) Release() {
 	if f.released {
 		log.Panicf("ino%d fh%d: double release", f.qIno.Ino, f.intFd())
 	}
-	f.fd.Close()
 	f.released = true
-	f.fdLock.Unlock()
-
 	openfiletable.Unregister(f.qIno)
+	f.fd.Close()
+	f.fdLock.Unlock()
 }
 
 // Flush - FUSE call