potential memory corruption due to size miscomputation upton custom region alloc init

[magenbluten]

here we allocate a fresh region with a user provided size value:

unbound/util/regional.c

Line 86 in 52b0480

struct regional* r = (struct regional*)malloc(size);

this size value gets aligned to the neccessary alignment requirements. but this happens after the malloc. thus size
can now be larger than what was actually allocated:

unbound/util/regional.c

Line 87 in 52b0480

size = ALIGN_UP(size, ALIGNMENT);

unbound/util/regional.c

Line 90 in 52b0480

r->first_size = size;

[gthess]

Seems like it indeed, thanks!