Should return 404 when the sourceMappingURL is not found

Steps to Reproduce

Enable source map, load a js file with sourceMappingURL but the map file is not found.
(see linked issue)

simpler reproducing steps, just try loading a source map URL
e.g.:
http://localhost:8080/zkau/web/something.js.map

Current Result

Exception

Expected Result

404 no found

Debug Information

the current implementation behaves differently depending on the debug-js config flag

<debug-js>true</debug-js> -> 500

<debug-js>false</debug-js> -> 404

also surprising are the different error response status codes/messages (compare for debugging purposes):

• http://localhost:8080/zkau/web/something.map -> 500 Exception
• http://localhost:8080/zkau/web/something.js -> 200 (window.zk&&zk.error?zk.error:alert)('/something.js not found');
• http://localhost:8080/zkau/web/something.css -> 404 not found

Workaround