also fix crypto::rand

Author: jeffro256

src/crypto/crypto.h

@@ -171,7 +171,9 @@ namespace crypto {
   /* Generate a value filled with random bytes.
    */
   template<typename T>
-  typename std::enable_if<std::is_pod<T>::value, T>::type rand() {
+  T rand() {
+    static_assert(std::is_standard_layout_v<T>, "cannot write random bytes into non-standard layout type");
+    static_assert(std::is_trivially_copyable_v<T>, "cannot write random bytes into non-trivially copyable type");
     typename std::remove_cv<T>::type res;
     generate_random_bytes_thread_safe(sizeof(T), (uint8_t*)&res);
     return res;