[8.1.2] All platform script errors lead to message "Unable to load ... does not appear to be a valid cordova platform"

When there is any problem in the platform scripts, e.g. because you deleted node_modules, you get this error:

```
MacBook-Pro:cordovaIos5Test2 sujan$ cordova build ios
Unable to load PlatformApi from platform. Error: Cannot find module 'unorm'
Unhandled error. (The platform "ios" does not appear to be a valid cordova platform. It is missing API.js. ios not supported.)
```

The first bit is true, but the second one not really.

Start by reproducing `cordova build ios` in the reported case where `node_modules` is missing, then trace the platform-loading error around `API.js`. Check how the initial `Cannot find module 'unorm'` failure becomes the later invalid-platform message. Done means platform script failures retain their actual cause instead of being reported as a missing or invalid Cordova platform.

Written by the indexing model from the issue text.