When falling back to vanilla recipes in the iteration of recipes,
a check is necessary to ensure that vanilla recipes are present.
RecipeIterator has been modified to account for the multi-map setup.
Due to vanilla blanket comparing data values, and the unspecified
order of hashmap iterators, we need to run through custom recipes
first, and therefore separately, to ensure that they are actually
used. By not adding the custom results to the experience table, we do
not override the experience gains from vanilla smelting recipes.
