fixed string_to_number

- fixed error message
- fixed good being used and replaced it with eof
- returns nan on error

src/util_string.h

@@ -63,16 +63,15 @@ string_contains(const std::string &s, unsigned char ch)
 }
 
 template <typename Precission>
-std::pair<bool, Precission>
+std::tuple<bool, Precission>
 string_to_number(const std::string &str)
 {
-  static_assert(std::is_arithmetic<Precission>::value,
-                "tokenize_comma_seperated_number_list can only produce float or double lists");
+  static_assert(std::is_arithmetic<Precission>::value, "Only arithmetic types allowed");
   std::stringstream ss(str);
-  Precission number = 0;
-  ss >> number;
 
-  if (ss.good()) { return { false, 0 }; }
+  Precission number = 0.0;
+  ss >> number;
+  if (!ss.eof()) { return { false, std::numeric_limits<Precission>::quiet_NaN() }; }
 
   return { true, number };
 }