Error if you press enter twice with Not Found displayed

[yukihirop]

Summary

Resolve #4

Test

Currently there are no tests.
Instead, the operation is guaranteed by executing the following command and actually checking the operation.

• python3 gfzs/views/not_found.py
• python3 gfzs/views/paging.py
• python3 gfzs/views/footer.py
• python3 gfzs/views/header.py
• python3 gfzs/views/search_result.py
• python3 gfzs/utils/markup.py
• python3 gfzs/utils/color.py
• python3 gfzs/config/app.py
• python3 gfzs/cmd/init.py
• python3 gfzs/cmd/edit.py
• python3 gfzs/cmd/demo.py
• python3 gfzs/cmd/valid.py
• python3 gfzs/controller.py
• python3 gfzs/model.py
• cat fixtures/rust.json | bin/gfzs -s 20
• cat fixtures/rust.json | python3 -m gfzs -s 40
• bin/gfzs init
• bin/gfzs edit
• bin/gfzs demo
• bin/gfzs valid
• black gfzs/**/*.py

[yukihirop]

LGTM