extmod/vfs_posix_file: Closing already closed file should not lead to error.
extmod/vfs_posix_file: Closing already closed file should not lead to error.

Similar to change in "native" file object of the Unix port.

Change-Id: I27fd32b812e270b061d9d15262d7e764c81d997b
Signed-off-by: Paul Sokolovsky <9dc5061f178bb11813e14f1ed02ba27eaf21fa5d@users.sourceforge.net>

pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython,pfalcon/micropython