The 'filename' parameter comes from user space and cannot be accessed
after calling ret = addrenv_select(binp->addrenv, &binp->oldenv); as
it changes the address environment and 'filename' points to who knows
where. In this case, calling nxtask_init(filename...) will cause a crash.
Solve this by making a local copy before changing address environment IF
argv = NULL. Why ? Because argv[0] contains the process name in this case
and the argument vector is already copied into kernel memory, thus
passing argv[0] to nxtask_init(argv[0]...) is safe.
0ef735f93a