Fix indentation in value_sett output

The character and size arguments where inverted.
The constructor used is `string (size_t n, char c);` the order can be
confusing because there is also a `string (const char* s, size_t n);`
constructor.

Author: romainbrenguier

src/pointer-analysis/value_set.cpp

@@ -211,7 +211,7 @@ void value_sett::output(std::ostream &out, const std::string &indent) const
       {
         out << ", ";
         if(width >= 40)
-          out << "\n" << std::string(' ', indent.size()) << "      ";
+          out << "\n" << std::string(indent.size(), ' ') << "      ";
       }
     }