Fix update check failing at random

Although this code contains many optimizations, the "actual" fix is on line 26 of `check_updates.gml`: upon doing an HTTP request, GameMaker sends multiple callbacks to inform async events about the "progress" of the request, during which the `status` field on `async_load` will be 1. The `result` will only be available when `status == 0` (success), so we must ONLY stop processing the callbacks (setting `update_http` to -1) when this occurs.

Previously, the script was setting `update_http` to -1 as soon as the first callback was received, which means `result` might not have been available yet. The `http_status` would also be `undefined` when this occurred, which meant that checking for the update would randomly fail.

Read more about it here: https://manual.yoyogames.com/GameMaker_Language/GML_Reference/Asynchronous_Functions/HTTP/http_get.htm
https://docs2.yoyogames.com/source/_build/2_interface/1_editors/events/async_events.html

Author: Bentroen

scripts/check_updates/check_updates.gml

@@ -8,39 +8,58 @@ function check_updates() {
 	// 2: up to date
 	// 4: downloading update
 
-	
-	var release = -1
-	try {
-		if (async_load[? "id"] = update_http) {
-		    update_http = -1
-		    if (async_load[? "http_status"] = 200) {
-		        var res = async_load[? "result"];
-				res = json_parse(res)
+	if (async_load[? "id"] = update_http) {
+		
+		// CHECK RECEIVED DATA:
+		// show_debug_message(async_load[? "result"])
+		// show_debug_message(async_load[? "status"])
+		// show_debug_message(async_load[? "http_status"])
+		
+		var status = async_load[? "status"];
+		
+		if (status == -1) { // error
+			update = -1
+			return;
+		}
+		
+		else if (status == 0) { // success
+			
+			if (async_load[? "http_status"] != 200) { // other status codes (403 - rate limit, etc.)
+				update = -1;
+				return;
+			}
+			
+			else {
+				update_http = -1;
+			
+			    var res = async_load[? "result"];
+				res = json_parse(res);
+
 				// Iterate array of releases and get the first (latest) release OR pre-release
+				var release = -1;
 				for (var i = 0; i < array_length(res); i++) {
 					if (check_prerelease || !res[i].prerelease) {
 						release = res[i];
-						break
+						break;
 					}
 				}
+			
+				if (release != -1) {
+					var new_version = string_replace(release.tag_name, "v", "");
+					if (new_version == version) {
+						update = 2;
+					} else {
+						if (question("Version " + new_version + " is available! Do you want to download it?", "Update available!")) {
+							var download_url = release.assets[0].browser_download_url;
+							update_download = http_get_file(download_url, update_file);
+							update = 4;
+						} else {
+							update = 1;
+						}
+					}
+				} else update = -1;
+			
 			}
 		}
-		if (release != -1) {
-			var new_version = string_replace(release.tag_name, "v", "")
-			if (new_version == version) {
-				update = 2
-			} else {
-				if (question("Version " + new_version + " is available! Do you want to download it?", "Update available!")) {
-					var download_url = release.assets[0].browser_download_url
-					update_download = http_get_file(download_url, update_file)
-					update = 4
-				} else {
-					update = 1
-				}
-			}
-		}
-	} catch (e) {
-		log("Update check failed: " + e.message + e.longMessage)
-		update = -1
 	}
 }