Log when OlmMachine returns unexpected value

Also condense the validity checks on the returned value

Author: AndrewFerr

src/e2ee/CryptoClient.ts

@@ -169,13 +169,12 @@ export class CryptoClient {
 
         await this.engine.lock.acquire(SYNC_LOCK_NAME, async () => {
             const syncResp = JSON.parse(await this.engine.machine.receiveSyncChanges(deviceMessages, deviceLists, otkCounts, unusedFallbackKeyAlgs));
-            if (Array.isArray(syncResp)) {
-                const decryptedToDeviceMessages = syncResp[0];
-                if (Array.isArray(decryptedToDeviceMessages)) {
-                    for (const msg of decryptedToDeviceMessages as IToDeviceMessage[]) {
-                        this.client.emit("to_device.decrypted", msg);
-                    }
+            if (Array.isArray(syncResp) && syncResp.length === 2 && Array.isArray(syncResp[0])) {
+                for (const msg of syncResp[0] as IToDeviceMessage[]) {
+                    this.client.emit("to_device.decrypted", msg);
                 }
+            } else {
+                LogService.error("CryptoClient", "OlmMachine.receiveSyncChanges did not return an expected value of [to-device events, room key changes]");
             }
 
             await this.engine.run();