How to reproduce:
1. In the attached "TestFor1091040.zip" project go to TestBuild -> Build
2. In the TestBuild.json file modify the "wasmCodeUrl" path to make it incorrect
3. Run the build in a browser
4. Open browser's console
5. Notice that the build doesn't load and there's no error indicating that the wasmCodeUrl path is invalid

Expected result: UnityLoader throws an error for an invalid path
Actual result: UnityLoader doesn't throw an error for an invalid path

Reproducible with: 2018.3.1f1, 2019.1.0a13

Note: UnityLoader.js has this code added to it for the error handling:
UnityLoader.Error.handler = function(e, t) {
console.log("Captured error: "+e);
}