Fixed issue #129 (#131)

+ Fixed unused variable warning
+ Added a `std::move` to avoid calling copy-assignment operator on non-copyable types

Co-authored-by: andy-byers <andrew.byers@utdallas.edu>

include/tl/expected.hpp

@@ -208,6 +208,7 @@ template <typename E>
 #ifdef TL_EXPECTED_EXCEPTIONS_ENABLED
   throw std::forward<E>(e);
 #else
+  (void)e;
 #ifdef _MSC_VER
   __assume(0);
 #else
@@ -824,7 +825,7 @@ struct expected_operations_base : expected_storage_base<T, E> {
       geterr().~unexpected<E>();
       construct(std::move(rhs).get());
     } else {
-      assign_common(rhs);
+      assign_common(std::move(rhs));
     }
   }