Fix constructing RegExp TypeError

[netil]

When dealing with multiple files and setting RegExp option, cause TypeError.

// webpack.config.js
module: {
	rules: [
                {
                    test: /\.js$/,
                    loader: "string-replace-loader",
                    options: {
                        multiple: [
				{ search: "foo", replace: "bar", flags: "g" },
			]
		}
	]
}

subquery param value is passed to processQuery() as below

• first call: { search: 'foo', replace: 'bar', flags: 'g' }
• next calls: { search: /foo/g, replace: 'bar', flags: 'g' }

Causing Module build failed: TypeError: Cannot supply flags when constructing one RegExp from another error.

This PR fix that issue

[Va1]

@netil
why would you supply both flags and regex search?