Avoid potential ambiguity in UrReturnHelper

If UrReturnHelper's operator() is explicitly called as
operator()<T>(...), there is a potential for ambiguity when the
specified RetType and the inferred T are the same: this is ambiguous
with the version of operator() where only T is a template parameter,
and T is specified explicitly. We already have code that explicitly
calls operator()<T>(...), so prevent this from becoming a problem.

Author: hvdijk

source/ur/ur.hpp

@@ -302,7 +302,8 @@ class UrReturnHelper {
 
   // Array return value where element type is differrent from T
   template <class RetType, class T>
-  ur_result_t operator()(const T *t, size_t s) {
+  typename std::enable_if<!std::is_same<RetType, T>::value, ur_result_t>::type
+  operator()(const T *t, size_t s) {
     return ur::getInfoArray<T, RetType>(s, param_value_size, param_value,
                                         param_value_size_ret, t);
   }