fix: only inject hmrId when HMR is enabled

Author: yyx990803

Diff for: src/hotReload.ts

@@ -7,6 +7,7 @@ export function genHotReloadCode(
   return `
 /* hot reload */
 if (module.hot) {
+  script.__hmrId = "${id}"
   const api = __VUE_HMR_RUNTIME__
   module.hot.accept()
   if (!api.createRecord('${id}', script)) {

Diff for: src/index.ts

@@ -184,7 +184,6 @@ const loader: webpack.loader.Loader = function(source: string) {
   }
 
   if (needsHotReload) {
-    code += `\nscript.__hmrId = "${id}"`
     code += genHotReloadCode(id, templateRequest)
   }