Eliminate 'dereference of null' CSA false warning in array_mark_proc

Eliminate 'dereference of null' CSA false warning in array_mark_proc

The exact warning message is: Access to field 'mse_start' results in a
dereference of a null pointer (loaded from variable 'new_mark_stack_ptr').

Note: the warning is eliminated regardless of assertion checking status.

* typd_mlc.c (GC_array_mark_proc): Call ABORT if mark_stack_ptr is NULL
(thus orig_mark_stack_ptr is ensured to be non-NULL after the check).