When calling `MEM_guarded_mallocN_aligned` with an alignment of 4,
a pointer that was returned that is 4 byte but not 8 byte aligned.
When freeing this pointer, `MEM_guarded_freeN` thinks that it is an
illegal pointer, because it asserts that `((intptr_t)memh) & 0x7 == 0`.
The fix is to always use at least 8 byte alignment.
Reviewers: brecht
Differential Revision: https://developer.blender.org/D5529
f2cab8267f