UserspaceEmulator: Default-initialize the siginfo struct used in waitid

Otherwise it'll have some random value from the stack, and the kernel
will not bother setting it to zero.
Also add a debug print and tweak the FIXME message.

Userland/DevTools/UserspaceEmulator/Emulator_syscalls.cpp

@@ -1358,15 +1358,16 @@ int Emulator::virt$waitid(FlatPtr params_addr)
  mmu().copy_from_vm(&params, params_addr, sizeof(params));
 
  Syscall::SC_waitid_params host_params = params;
- siginfo info;
+ siginfo info {};
  host_params.infop = &info;
 
  int rc = syscall(SC_waitid, &host_params);
  if (rc < 0)
  return rc;
 
  if (info.si_addr) {
- // FIXME: Translate this somehow.
+ // FIXME: Translate this somehow once we actually start setting it in the kernel.
+ dbgln("si_addr is set to {:p}, I did not expect this!", info.si_addr);
  TODO();
  }