L1VM - security fixes

I did fix some issues in my module function call code. And in my JIT-compiler. Now it is checked if a module function was set at the given index. The VM now exits with an error if no function was set!
The JIT-compiler now checks if there is no compiled code in a call index. The VM will now exit with an error if no code was found! Now my L1VM is more secure than before. I recommend to upgrade your L1VM to the latest release on GitHub.