refactor: check update jar existence instead of flag

Author: bouclem

src/main/java/org/mcphackers/mcp/tasks/TaskDownloadUpdate.java

@@ -36,19 +36,17 @@ protected Stage[] setStages() {
 						boolean confirmed = mcp.updateDialogue(notes, latestVersion);
 						if (confirmed) {
 							log("Downloading update...");
-							boolean downloaded = false;
 							for (Object obj : releaseJson.getJSONArray("assets")) {
 								if (obj instanceof JSONObject) {
 									JSONObject assetObj = (JSONObject) obj;
 									if (!assetObj.getString("name").endsWith(mcp.isGUI() ? "-GUI.jar" : "-CLI.jar")) {
 										continue;
 									}
 									FileUtil.downloadFile(assetObj.getString("browser_download_url"), Paths.get(MCPPaths.UPDATE_JAR));
-									downloaded = true;
 									break;
 								}
 							}
-							if (!downloaded) {
+							if (!Files.exists(Paths.get(MCPPaths.UPDATE_JAR))) {
 								IOException t = new IOException("No matching update asset found in release! Aborting");
 								Util.throwExceptionInIDE(t);
 								throw t;