Change type of scoped_input_handler::m_quit_handler

Change type of scoped_input_handler::m_quit_handler

Simon pointed out that scoped_input_handler::m_quit_handler must have
the correct scoped_restore_tmpl type, to avoid binding to a temporary.
This patch fixes the problem.

gdb/ChangeLog
2017-09-22  Tom Tromey  <tom@tromey.com>

	* utils.c (class scoped_input_handler) <m_quit_handler>: Change
	type to scoped_restore_tmpl.
	<scoped_input_handler>: Initialize m_quit_handler directly.

Reviewed-By: Pedro Alves <palves@redhat.com>