Fix a Chromium based glitch (#1856)

* Force HTTP stack response for Chromium based browsers so their messages show up properly since they still have native .user.js and probably a bugged interpretation of a valid response for no Content-Type. Gecko always returns a blank page no matter the setting at this time. Note this is not needed for 304 which is also a HTTP stack response. Plus they've had this issue in the past with other status codes.
* Usually Chromium based browsers seem to think the "...site can't be reached... ERR_INVALID_RESPONSE"... this changes that to "Access to localhost was denied\nYou don't have authorization to view this page.\nHTTP ERROR 403"
* Not all engines properly detect HTML content vs actual JavaScript type which is one of the reasons why it's pure response status codes. Additionally the standard Warning header is already put out instead of wasting unnecessary bandwidth/processes.

Applies to https://openuserjs.org/scripts/omgmikey/Chaturbate_Easy_Tipping/issues/when_i_try_to_download_this_script_it_says_page_is_missing#comment-17d4b1769c4 and post #1847

controllers/scriptStorage.js

@@ -576,6 +576,10 @@ exports.sendScript = function (aReq, aRes, aNext) {
       aRes.set('Warning', '199 ' + aReq.headers.host +
         rfc2047.encode(' Invalid @updateURL') +
           (process.env.FORCE_BUSY_UPDATEURL_CHECK === 'true' ? ' in lockdown.' : '.'));
+
+      // NOTE: Force HTTP stack response for Chromium based browsers #1856
+      aRes.set('Content-Type', 'text/html; charset=UTF-8');
+
       aRes.status(403).send(); // Forbidden
       return;
     }