'pid' cannot really be used uninitialized, but Clang analyzer does not
see it. Add initializer to silence it and also make debugging slightly
easier.
Explicitly set pid's address to NULL to fix this complaint:
"Address of stack memory associated with local variable 'pid' is still
referred to by the global variable 'g_spawn_parms' upon returning to
the caller."
No functional change.
Signed-off-by: Juha Niskanen <juha.niskanen@haltian.com>