Not a big deal, but here is a slightly better fix that avoids adding
some spaces before the closing }.

The difference wrt to the previous one is just:

-           (unless (memq (caar tbl) '(:endgroup :endgrouptag)) (insert "\n"))
-           (when (or ingroup intaggroup) (insert "  "))
+           (unless (memq (caar tbl) '(:endgroup :endgrouptag))
+             (insert "\n")
+             (when (or ingroup intaggroup) (insert "  ")))

That is, the when clause is inside the unless clause.