fix: abort update when no matching asset is found

Fixes #217 (followup). When the GitHub release assets do not contain a jar matching the running mode (-GUI.jar or -CLI.jar), the loop previously exited silently, then the code spawned the Update process pointing at a non-existent update.jar and called System.exit(0). The user saw RetroMCP just close with no feedback. Now the update aborts with a clear IOException, surfaced through the standard task error dialog.

Author: bouclem

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

@@ -36,16 +36,23 @@ 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) {
+								IOException t = new IOException("No matching update asset found in release! Aborting");
+								Util.throwExceptionInIDE(t);
+								throw t;
+							}
 							Path jarPath = Paths.get(MCP.class
 									.getProtectionDomain()
 									.getCodeSource()