Fix exception when homeDir is not available

[kaykayehnn]

I encountered a crash when running live-server from a systemd service, and tracked the issue to loading the config from a user's home folder

live-server/live-server.js

Lines 17 to 23 in 01cd7f9

	var homeDir = process.env[(process.platform === 'win32') ? 'USERPROFILE' : 'HOME'];
	var configPath = path.join(homeDir, '.live-server.json');
	if (fs.existsSync(configPath)) {
	var userConfig = fs.readFileSync(configPath, 'utf8');
	assign(opts, JSON.parse(userConfig));
	if (opts.ignorePattern) opts.ignorePattern = new RegExp(opts.ignorePattern);
	}

In systemd services, the HOME variable is not present, which causes the issue.

This PR fixes it by verifying the variable is non-empty before loading a user's config.

[belauzas]

Hi @kaykayehnn I would like to use your PR for dead-server update, because this project seems to be abandoned.