fix: stylePostLoader injection for windows flat node_modules

close #1284

Author: yyx990803

lib/loaders/pitcher.js

@@ -13,7 +13,7 @@ module.exports.pitch = function (remainingRequest) {
   const loaders = this.loaders.slice(1) // remove self
 
   // do not inject if user uses null-loader to void the type (#1239)
-  if (loaders.some(l => /(\/|\\)null-loader/.test(l.path))) {
+  if (loaders.some(l => /(\/|\\|@)null-loader/.test(l.path))) {
     return
   }
 
@@ -45,8 +45,8 @@ module.exports.pitch = function (remainingRequest) {
 
   // Inject style-post-loader before css-loader for scoped CSS and trimming
   if (query.type === `style`) {
-    const cssLoaderIndex = loaders.findIndex(l => /(\/|\\)css-loader/.test(l.path))
-    if (cssLoaderIndex) {
+    const cssLoaderIndex = loaders.findIndex(l => /(\/|\\|@)css-loader/.test(l.path))
+    if (cssLoaderIndex > -1) {
       const afterLoaders = loaders.slice(0, cssLoaderIndex + 1)
       const beforeLoaders = loaders.slice(cssLoaderIndex + 1)
       const request = genRequest([