malloc_usable_size should not be called with pointer from new

maloc_usable_size should be used to get the size of the underlying allocation returned from "malloc with friends". There is no guarantee that it would work with a pointer returned from the new operator (according to various searches it is "undefined')

"Note that applying malloc_usable_size (or _msize) to the result of new is undefined behavior." (https://stackoverflow.com/questions/54783860/getting-size-of-dynamic-c-style-array-vs-use-of-delete-contradiction