Additional low-level cleanups (2)

Additional low-level cleanups (2)

* More `while (1)` becomes `while (true)`
* More use of `ptr != nullptr` in conditionals
* Also `handle!=nullptr`in conditionals
* Also `while (ptr)` becomes `while (ptr != nullptr)`
* Add `{ ... }` brackets to a `do ... while()`
* Some `while(int)` changed to `while (int!=0)`