vm: check invalid allocation sizes of non 64bits platform
vm: check invalid allocation sizes of non 64bits platform

The public API of the NSL uses `u64` (for portability reasons). But on
32bits platforms for examples, the value might overflow.

nany-lang/nany,milipili/nany,nany-lang/nanyc,nany-lang/nany,milipili/nany,nany-lang/nanyc,milipili/nany,nany-lang/nanyc,nany-lang/nany