Allow delete_array(nullptr) and delete_(nullptr)

[Dan Bonachea]

From C++14 [expr.delete]:

In the first alternative (delete object), the value of the operand of delete may be a null pointer value, a pointer to a non-array object created by a previous new-expression, [...]. In the second alternative (delete array), the value of the operand of delete may be a null pointer value or a pointer value that resulted from a previous array new-expression.

However our current Preconditions for upcxx::delete_(g) and upcxx::delete_array(g) include:

g must be a non-deallocated pointer

We should expand this precondition to mirror the behavior of C++ delete, so that we accept delete_array(nullptr) and delete_(nullptr) and treat them as no-ops.

[Dan Bonachea]

I've verified the implementation already contains the null checks to handle this correctly, although there are no tests for this functionality.

[Amir Kamil]

Allow delete_() and delete_array() to be invoked on a null pointer. This fixes Issue #114.

→ <<cset 0d52695dba29>>