Fix gstat's interactive f and q commands

curses and libedit don't play well together. After last year's libedit
upgrade in head, they play even less well together. This change resets some
curses settings after they get screwed up by libedit calls. Without it,
gstat's interactive commands require an extra "enter", screw up the terminal
on exit, and screw up the display if the user enters an invalid filter
string.

PR: 204852
Submitted by: Keith White
Reviewed by: pfg
Approved by: re (gjb)
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D6934