Save the environment.

Save the environment.

Before the previous two commits we used to read the environment from the
registry and set it using an optimisation which modified the retrieved
block in-place.

Now we need to set the environment twice after querying the registry -
once in get_parameters() and once just before CreateProcess(), which
means we can't use the in-place optimisation and must copy the block
before operating on it.

Additionally, nssm_hook() cleans the environment so we have to reinstate
it immediately prior to launching the application.