Added error handling for non-CORS requests.

Author: n1474335

src/core/config/OperationConfig.js

@@ -3407,7 +3407,7 @@ const OperationConfig = {
             "<br><br>",
             "You can add headers line by line in the format <code>Key: Value</code>",
             "<br><br>",
-            "This operation will throw an error for any status code that is not 200, unless the 'Ignore status code' option is checked.",
+            "The status code of the response, along with a limited selection of exposed headers, can be viewed by checking the 'Show response metadata' option. Only a limited set of response headers are exposed by the browser for security reasons.",
         ].join("\n"),
         run: HTTP.runHTTPRequest,
         inputType: "string",

src/core/operations/HTTP.js

@@ -126,6 +126,10 @@ const HTTP = {
 
         return fetch(url, config)
         .then(r => {
+            if (r.status === 0 && r.type === "opaque") {
+                return "Error: Null response. Try setting the connection mode to CORS.";
+            }
+
             if (showResponseMetadata) {
                 let headers = "";
                 for (let pair of r.headers.entries()) {