src/usermod.c: update_group_file(): Reduce scope of local variable

src/usermod.c: update_group_file(): Reduce scope of local variable

After _every_ iteration, 'changed' is always 'false'.  We don't need to
have it outside of the loop.

See:

$ grepc update_group_file . \
| grep -e changed -e goto -e continue -e break -e free_ngrp -e '{' -e '}' \
| pcre2grep -v -M '{\n\t*}';
{
	bool                changed;
	changed = false;
	while ((grp = gr_next ()) != NULL) {
		if (!was_member && !is_member) {
			continue;
		}
		if (was_member) {
			if ((!Gflg) || is_member) {
				if (lflg) {
					changed = true;
				}
			} else {
				changed = true;
			}
		} else if (is_member) {
			changed = true;
		}
		if (!changed)
			goto free_ngrp;
		changed = false;
free_ngrp:
	}
}

This was already true in the commit that introduced the code:

$ git show 45c6603cc:src/usermod.c \
| grepc update_group \
| grep -e changed -e goto -e break -e continue -e '\<if\>' -e '{' -e '}' \
| pcre2grep -v -M '{\n\t*}';
{
	int changed;
	changed = 0;
	while ((grp = gr_next())) {
		 * See if the user specified this group as one of their
		if (!was_member && !is_member)
			continue;
		if (was_member && (!Gflg || is_member)) {
			if (lflg) {
				changed = 1;
			}
		} else if (was_member && Gflg && !is_member) {
			changed = 1;
		} else if (!was_member && Gflg && is_member) {
			changed = 1;
		}
		if (!changed)
			continue;
		changed = 0;
	}
}

Fixes: 45c6603cc86c ("[svn-upgrade] Integrating new upstream version, shadow (19990709)")
Signed-off-by: Alejandro Colomar <alx@kernel.org>