Heap: Just align it on a 16-byte boundary if it's not aligned

kernel/src/memory/Heap.cpp

@@ -85,8 +85,7 @@ static usize get_fair_offset_to_split_at(HeapBlock* block, usize min)
     available -= (available /
                   2); // reserve half of the rest for the new block, while still leaving another half for the old one.
 
-    check(is_aligned(available,
-                     16UL)); // If necessary, we can just align it. This is more of a sanity check than a requirement.
+    available = align_down(available, 16UL); // Everything has to be aligned on a 16-byte boundary
 
     return available + block->req_size;
 }