SSR module load errors are not handled

[Rich-Harris]

Describe the bug

The following code...

try {
  const mod = await server.ssrLoadModule('/non-existent');
  do_something_with(mod);
} catch (e) {
  // error is handled, no warning should appear
}

...results in this:

UnhandledPromiseRejectionWarning: Error: failed to load module for ssr: /non-existent

Reproduction

package.json

{
  "scripts": {
    "start": "node server.js"
  },
  "devDependencies": {
    "vite": "^2.0.1"
  },
  "type": "module"
}

server.js

import vite from 'vite';

async function main() {
  const server = await vite.createServer();

  try {
    await server.ssrLoadModule('/non-existent');
  } catch (e) {
    console.error('handled', e);
  }
}

main();

Expected result: it prints 'handled' along with the error. Actual result: it prints 'handled' alongside the unhandled promise rejection warning.

The culprit is this line...

vite/packages/vite/src/node/ssr/ssrModuleLoader.ts

Line 49 in 8ed67cf

modulePromise.then(() => pendingModules.delete(url))

...which needs a catch:

-modulePromise.then(() => pendingModules.delete(url))
+modulePromise.catch(() => {}).then(() => pendingModules.delete(url))

System Info

• vite version: 2.0.3
• Operating System: MacOS
• Node version: 12.21.0
• Package manager (npm/yarn/pnpm) and version: npm 7.5.6