fix hang in pinentry prompt due to stderr blocking

Closing stderr causes pinentry to block forever if it wants to log
something -- for example pinentry-gtk-2 emits this error on some installs:

(pinentry:20274): GLib-GObject-CRITICAL **: Object class GtkSecureEntry
doesn't implement property 'editing-canceled' from interface
'GtkCellEditable'

As a result, after the GETPIN command is issued, pinentry hangs when
trying to display the window, and is not possible to login with lpass
without disabling pinentry via the environment variable.

Just leave stderr open to fix.

Signed-off-by: Bob Copeland <copeland@lastpass.com>