message: XPath: Simplify evaluation error flow
  Instead of having two checks for out-of-memory when exceptions are
  enabled, do just one and decide what to do based on whether we can
  throw.
diff: @@ -11823,11 +11823,16 @@ PUGI__NS_BEGIN
  xpath_string r = impl->root->eval_string(c, sd.stack);
  - #ifndef PUGIXML_NO_EXCEPTIONS
  - if (sd.oom) throw std::bad_alloc();
  + if (sd.oom)
  + {
  + #ifdef PUGIXML_NO_EXCEPTIONS
  + return xpath_string();
  + #else
  + throw std::bad_alloc();
  #endif
  + }
  - return sd.oom ? xpath_string() : r;
  + return r;
  }
  PUGI__FN impl::xpath_ast_node* evaluate_node_set_prepare(xpath_query_impl* impl)
  @@ -12463,11 +12468,16 @@ namespace pugi
  bool r = static_cast<impl::xpath_query_impl*>(_impl)->root->eval_boolean(c, sd.stack);
  - #ifndef PUGIXML_NO_EXCEPTIONS
  - if (sd.oom) throw std::bad_alloc();
  + if (sd.oom)
  + {
  + #ifdef PUGIXML_NO_EXCEPTIONS
  + return false;
  + #else
  + throw std::bad_alloc();
  #endif
  + }
  - return sd.oom ? false : r;
  + return r;
  }
  PUGI__FN double xpath_query::evaluate_number(const xpath_node& n) const
  @@ -12479,11 +12489,16 @@ namespace pugi
  double r = static_cast<impl::xpath_query_impl*>(_impl)->root->eval_number(c, sd.stack);
  - #ifndef PUGIXML_NO_EXCEPTIONS
  - if (sd.oom) throw std::bad_alloc();
  + if (sd.oom)
  + {
  + #ifdef PUGIXML_NO_EXCEPTIONS
  + return impl::gen_nan();
  + #else
  + throw std::bad_alloc();
  #endif
  + }
  - return sd.oom ? impl::gen_nan() : r;
  + return r;
  }
  #ifndef PUGIXML_NO_STL
  @@ -12527,11 +12542,16 @@ namespace pugi
  impl::xpath_node_set_raw r = root->eval_node_set(c, sd.stack, impl::nodeset_eval_all);
  - #ifndef PUGIXML_NO_EXCEPTIONS
  - if (sd.oom) throw std::bad_alloc();
  + if (sd.oom)
  + {
  + #ifdef PUGIXML_NO_EXCEPTIONS
  + return xpath_node_set();
  + #else
  + throw std::bad_alloc();
  #endif
  + }
  - return sd.oom ? xpath_node_set() : xpath_node_set(r.begin(), r.end(), r.type());
  + return xpath_node_set(r.begin(), r.end(), r.type());
  }
  PUGI__FN xpath_node xpath_query::evaluate_node(const xpath_node& n) const
  @@ -12544,11 +12564,16 @@ namespace pugi
  impl::xpath_node_set_raw r = root->eval_node_set(c, sd.stack, impl::nodeset_eval_first);
  - #ifndef PUGIXML_NO_EXCEPTIONS
  - if (sd.oom) throw std::bad_alloc();
  + if (sd.oom)
  + {
  + #ifdef PUGIXML_NO_EXCEPTIONS
  + return xpath_node();
  + #else
  + throw std::bad_alloc();
  #endif
  + }
  - return sd.oom ? xpath_node() : r.first();
  + return r.first();
  }
  PUGI__FN const xpath_parse_result& xpath_query::result() const
  