[MMBotMDHacking] Fix a deadlock in Asm68kCommand

The **ChangeDirectory()** method uses a monitor to avoid multiple threads from changing the current directory concurrently, and **RestoreDirectory()** releases the monitor. **Asm68kCommand** did not use a try-finally block to call **RestoreDirectory()**, so the lock could remain acquired if an exception is thrown before **RestoreDirectory()** is called.