[binutils-gdb] Use a scoped_restore for command_nest_depth

[sergiodj+buildbot@sergiodj.net]

*** TEST RESULTS FOR COMMIT b51b225eb9b03b627967108ee3de38ada5de219d ***

Author: Tom Tromey <tom@tromey.com>
Branch: master
Commit: b51b225eb9b03b627967108ee3de38ada5de219d

Use a scoped_restore for command_nest_depth

This changes a couple of places to use a scoped_restore when
manipulating command_nest_depth.

ChangeLog
2017-08-03  Tom Tromey  <tom@tromey.com>

	* cli/cli-script.c (execute_user_command)
	(execute_control_command): Use scoped_restore.