Zero-length ManagedArrays leak memory

[ajkunen]

We've seen an issue with CHAI allocating zero-sized arrays. We see them report as memory leaks using gcc memory sanitizer, and also with valgrind.

We can see this on a CPU-only build with the default malloc Umpire allocator.

[ajkunen]

Just a note: this is a leak in CHAI, not Umpire