fix: build/show dummy component for empty files in order not to abort build /ファイルが空の場合は仮コンポーネントをビルドしてビルドエラーを避ける

[vladinomo]

Summary 概要

Fix for #199

• The problem comes from reference to undefined attributes created by parsing empty html/spear files. To avoid it. in case of parsing empty files, the script inserts a dummy component.

Spec

• shows <div>a component {component name} is empty.</div> on the web page

Another problem

with this change, spear watch won't stop with empty components but logger showing error messages below

[Page]: /index
BadRequestError: Bad Request
    at createHttpError (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/send/index.js:979:12)
    at SendStream.error (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/send/index.js:270:31)
    at SendStream.pipe (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/send/index.js:516:10)
    at /Users/name/Documents/projects/spear/packages/spear-cli/node_modules/live-server/index.js:97:5
    at call (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/connect/index.js:239:7)
    at next (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/connect/index.js:183:5)
    at Function.handle (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/connect/index.js:186:3)
    at Server.app (/Users/name/Documents/projects/spear/packages/spear-cli/node_modules/connect/index.js:51:37)
    at Server.emit (node:events:390:28)
    at parserOnIncoming (node:_http_server:951:12)