user-info.eclass: egetent: fix lookup by id when ROOT != /

Previous to this change, egetent would match any id that starts with the
id given as input. For example:

egetent group 1

bin::1:root,bin,daemon
wheel::10:root
floppy::11:root
news::13:news
uucp::14:uucp
console::17:
audio::18:
cdrom::19:
users:💯

Adding a colon to the grep expression yields the desired result:

egetent group 1

bin::1:root,bin,daemon

Signed-off-by: Mike Gilbert <floppym@gentoo.org>

eclass/user-info.eclass

@@ -1,4 +1,4 @@
-# Copyright 1999-2022 Gentoo Authors
+# Copyright 1999-2023 Gentoo Authors
 # Distributed under the terms of the GNU General Public License v2
 
 # @ECLASS: user-info.eclass
@@ -64,7 +64,7 @@ egetent() {
 			getent "${db}" "${key}"
 		else
 			if [[ ${key} =~ ^[[:digit:]]+$ ]]; then
-				grep -E "^([^:]*:){2}${key}" "${ROOT}/etc/${db}"
+				grep -E "^([^:]*:){2}${key}:" "${ROOT}/etc/${db}"
 			else
 				grep "^${key}:" "${ROOT}/etc/${db}"
 			fi