Simplify geometry_n function

Author: joto

src/geom-functions.cpp

@@ -70,13 +70,13 @@ class geometry_n_visitor
 
     void operator()(geom::collection_t const &input) const
     {
-        *m_output = input[m_n - 1];
+        *m_output = input[m_n];
     }
 
     template <typename T>
     void operator()(geom::multigeometry_t<T> const &input) const
     {
-        m_output->set<T>() = input[m_n - 1];
+        m_output->set<T>() = input[m_n];
     }
 
     template <typename T>
@@ -95,13 +95,13 @@ class geometry_n_visitor
 
 void geometry_n(geometry_t *output, geometry_t const &input, std::size_t n)
 {
-    auto const num = num_geometries(input);
-    if (n < 1 || n > num) {
+    auto const max = num_geometries(input);
+    if (n < 1 || n > max) {
         output->reset();
         return;
     }
 
-    input.visit(geometry_n_visitor{output, n});
+    input.visit(geometry_n_visitor{output, n - 1});
     output->set_srid(input.srid());
 }