libcroco parser: limit recursion in block and any productions
If we don't have any limits, we can recurse forever and overflow the stack. This is for CVE-2020-12825: Stack overflow in cr_parser_parse_any_core in cr-parser.c. Bug: https://gitlab.gnome.org/Archive/libcroco/-/issues/8 Patch from https://gitlab.gnome.org/Archive/libcroco/-/merge_requests/5