* Furnace would say it was overloaded when it had a non-cookable source

* I didn't understand that expression last fix and now the furnace would burn fuel
even when it had no source item.

src/content_nodemeta.cpp

@@ -182,7 +182,7 @@ std::string FurnaceNodeMetadata::infoText()
  assert(src_list);
  const InventoryItem *src_item = src_list->getItem(0);
 
- if(src_item) {
+ if(src_item && src_item->isCookable()) {
  InventoryList *dst_list = m_inventory->getList("dst");
  if(!dst_list->roomForCookedItem(src_item))
  return "Furnace is overloaded";
@@ -284,17 +284,17 @@ bool FurnaceNodeMetadata::step(float dtime)
  }
  changed = true;
 
- // Fall through if the fuel item was used up this step
+ // If the fuel was not used up this step, just keep burning it
  if(m_fuel_time < m_fuel_totaltime)
  continue;
  }
 
  /*
- If there is no source item or source item is not cookable,
- or furnace became overloaded, stop loop.
+ If there is no source item, or the source item is not cookable,
+ or the furnace is still cooking, or the furnace became overloaded, stop loop.
  */
- if((m_fuel_time < m_fuel_totaltime || (src_item && dst_list->roomForCookedItem(src_item) == false))
- && (src_item == NULL || m_src_totaltime < 0.001))
+ if(src_item == NULL || !room_available || m_fuel_time < m_fuel_totaltime ||
+ dst_list->roomForCookedItem(src_item) == false)
  {
  m_step_accumulator = 0;
  break;