Ticket #3176: sftpfs: fix segfault when trying to view a file.

Segfault was caused by using data from already free()-d memory
in /src/vfs/sftpfs/file.c. sftpfs_lseek() accessed a memory block,
which was previously deallocated by sftpfs_reopen().

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>
Merge branch '3176_sftpfs_view_file_segfault'

* 3176_sftpfs_view_file_segfault:
  Ticket #3176: sftpfs: fix segfault when trying to view a file.