Add DStr move assignment operator

libobs/util/dstr.hpp

@@ -31,6 +31,12 @@ public:
 		dstr_move(&str, &other.str);
 	}
 
+	inline DStr &operator=(DStr &&other)
+	{
+		dstr_move(&str, &other.str);
+		return *this;
+	}
+
 	inline ~DStr() {dstr_free(&str);}
 
 	inline operator dstr*()             {return &str;}