enter: Fix support for Active Directory usernames including backslashes. Fix #1360

Signed-off-by: Luca Di Maio <luca.dimaio1@gmail.com>

distrobox-enter

@@ -79,7 +79,8 @@ fi
 # Defaults
 container_command=""
 # by default we use getent to get the login shell of the user and use that
-container_command_login="/bin/sh -c \"\\\$(getent passwd ${USER} | cut -f 7 -d :) -l\""
+container_command_user="$(echo "${USER}" | sed 's|\\|\\\\|g')"
+container_command_login="/bin/sh -c \"\\\$(getent passwd ${container_command_user} | cut -f 7 -d :) -l\""
 container_image_default="registry.fedoraproject.org/fedora-toolbox:39"
 container_manager="autodetect"
 container_manager_additional_flags=""