Always register custom singularity oredict recipes

[WaitingIdly]

resolve #31
because fba62b6 moved registering custom singularity recipes into preInit, any oredict created afterwards (eg crafttweaker) wouldnt register a singularity due to over-cautious validation checks. however, if a singularity is registered to an oredict that doesnt exist/has no items: nothing bad happens. in fact, this happens by default in ItemSingularity.java, since it tries to register a singularity to ingotArdite, and the dev environment doesnt have any ingotArdite.
as such, this PR changes ItemSingularityCustom.java to always register oredict singularities, even when the oredict doesnt exist or has no items.

tested with

    S:custom_singularities <
        101;experience;ore:itemXP;b3f43b
     >

and both with and without

<ore:itemXP>.add(<minecraft:dirt>);