Fix maybe again for non-copy/move types

Author: stevenwdv

Rx/v2/src/rxcpp/rx-util.hpp

@@ -637,19 +637,19 @@ class maybe
 
     template<class U = T>
     void reset(U&& value) {
-        *this = std::forward<U>(value);
+        val_.emplace(std::forward<U>(value));
     }
 
     maybe& operator=(const maybe& other) = default;
     maybe& operator=(maybe&& other) = default;
 
     maybe& operator=(const T& value) {
-        val_ = value;
+        reset(value);
         return *this;
     }
 
     maybe& operator=(T&& value) {
-        val_ = std::move(value);
+        reset(std::move(value));
         return *this;
     }
 };