forall.py: Close file after removing the stream

In order to remove the stream fileno() will be called on the filedescriptor.
If the file is already closed fileno() will raise an error and forall
will fail.

Bug: https://crbug.com/gerrit/12563
Change-Id: Ib7b895fe881c844e3eb3672b011fdcdbdae63024
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/262838
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
Tested-by: Karsten Pfeiffer-Raddatz <raddatz.karsten@gmail.com>