lisp-format: Fix a crash in format string that contains "~@?" before "~V".
* gettext-tools/src/format-lisp.c (nocheck_params): Don't call
add_req_type_constraint if position < 0.
* gettext-tools/tests/xgettext-lisp-5: New file.
* gettext-tools/tests/Makefile.am (TESTS): Add it.
