check if connected to vm before uploading

src/index.ts

@@ -80,6 +80,10 @@ app.put("/:vm/:filename", async (req, res) => {
         res.status(400);
         return { success: false, result: "Filename contains disallowed characters" };
     }
+    if (!VMs.get(vm)!.isConnectedToVM) {
+        res.status(503);
+        return { success: false, result: "Not connected to VM (make sure the agent is running)" };
+    }
     if (IPs.has(req.ip)) {
         if (!IPs.get(req.ip)!.Limit()) {
             res.status(429);