guix-install.sh: Directly exit in case of errors in chk_require.

* etc/guix-install.sh (chk_require): Directly exit in case of errors in
chk_require, instead of relying on 'set -e'.

etc/guix-install.sh

@@ -121,10 +121,8 @@ chk_require()
         command -v "$c" &>/dev/null || warn+=("$c")
     done
 
-    [ "${#warn}" -ne 0 ] &&
-        { _err "${ERR}Missing commands: ${warn[*]}.";
-          return 1; }
-    
+    [ "${#warn}" -ne 0 ] && die "Missing commands: ${warn[*]}."
+
     _msg "${PAS}verification of required commands completed"
 }