mi_heap_realloc_aligned does not respect alignment

Hello,

I noticed this in mimalloc 1.7.6:

static void* mi_heap_realloc_zero_aligned(mi_heap_t* heap, void* p, size_t newsize, size_t alignment, bool zero) mi_attr_noexcept {
  mi_assert(alignment > 0);
  if (alignment <= sizeof(uintptr_t)) return _mi_heap_realloc_zero(heap,p,newsize,zero);
  size_t offset = ((uintptr_t)p % alignment); // use offset of previous allocation (p can be NULL)
  return mi_heap_realloc_zero_aligned_at(heap,p,newsize,alignment,offset,zero);
}

However, if the previously allocated ptr did not use any alignment constraint, we use an unwanted offset when allocating the new block and thus return a value which is not correctly aligned.
Is that intentional?

Start at mi_heap_realloc_zero_aligned in the issue snippet and inspect how its offset is derived when reallocating an unaligned pointer with an alignment requirement. Reproduce that case and verify that the resulting pointer satisfies the requested alignment; add or update coverage for the behavior if the repository has a relevant allocator test.