Introduce kreallocarray with overflow checking

[ethomson]

Introduce a kreallocarray with overflow checking, with a signature equivalent to OpenBSD reallocarray(3). This prevents a realloc from appearing to succeed when new_n_buckets is larger than SIZE_MAX / sizeof(khkey_t) or SIZE_MAX / sizeof(khval_t).

[noporpoise]

I think that - should be a /

-#define kreallocarray(P,N,Z) ((SIZE_MAX - N < Z) ? NULL : krealloc(P, (N*Z)))
+#define kreallocarray(P,N,Z) ((SIZE_MAX / N < Z) ? NULL : krealloc(P, (N*Z)))

[ethomson]

Thanks @noporpoise - that - should indeed be a /. Fixed!