vite: fix https is enabled if cert is not present

vite.config.ts

@@ -88,13 +88,15 @@ export default defineConfig(({ mode }) => {
       version(),
     ],
     server: {
-      https: {
+      https: serverHttpCertBase
+        ? {
             // This config controls https for the *dev server*.
             // See docs/dev-https.md for setting up https
             key: serverHttpCertKey,
             cert: serverHttpCertCrt,
             passphrase: serverHttpCertPassword,
-      },
+          }
+        : undefined,
     },
     define: {
       "import.meta.env.BUILT_AT": `"${new Date().toISOString()}"`,