HPCC-12031 Always throw exceptions if cannot allocate enough memory

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
No, it was deliberately changed - as part of the work to allow HEAP_ALIGNMENT_SIZE to be changed to something other than 0x100000.  It ensures there is still sufficient memory to allocate the items expected in the tests.