Check if `size == 0` in `safe_malloc_function()`
Check if `size == 0` in `safe_malloc_function()`

If the size passed to `safe_malloc` is zero, return NULL. This also prevents `safe_malloc` from exiting if zero is passed, while memory allocation succeeded.

VanJanssen/safe-c,ErwinJanssen/elegan-c,VanJanssen/elegan-c