do not mix base address with size of a value

[tshepang]

Reference does not make this guarantee

[kirtchev-adacore]

Indeed, the Reference no longer has similar rules. The only closest things they have is alloc-limit, which Tshepang has included in the PR.

Note that it is also possible to delete :dp:fls_kaomYy0Ml4Nh since all uses of "base address" have now disappeared.

[tshepang]

there is one user

It is undefined behavior to create an llocated object at base address null