Call FlushInstructionCache after manipulating assembly

As described in the documentation of the win32 api [FlushInstructionCache](https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-flushinstructioncache):

> Applications should call FlushInstructionCache if they generate or modify code in memory. The CPU cannot detect the change, and may execute the old code it cached.