fix: throw when refresh runtime is loaded twice (fix #101)

Author: ArnaudBarre

packages/plugin-react/src/refreshUtils.js

@@ -1,3 +1,13 @@
+/* eslint-disable no-undef */
+if (typeof window !== 'undefined') {
+  if (window.__vite_plugin_react_runtime_loaded__) {
+    throw new Error(
+      'React refresh runtime was loaded twice. Maybe you forgot the base path?',
+    )
+  }
+  window.__vite_plugin_react_runtime_loaded__ = true
+}
+
 function debounce(fn, delay) {
   let handle
   return () => {
@@ -6,7 +16,6 @@ function debounce(fn, delay) {
   }
 }
 
-/* eslint-disable no-undef */
 const enqueueUpdate = debounce(exports.performReactRefresh, 16)
 
 // Taken from https://github.com/pmmmwh/react-refresh-webpack-plugin/blob/main/lib/runtime/RefreshUtils.js#L141