Prussian Blue Paint crashes when you don't have a card to upgrade

[bug-sniper]

When you try to upgrade a curse without an unupgraded card, you get this error:

java.lang.IllegalArgumentException: n must be positive
at com.badlogic.gdx.math.RandomXS128.nextLong(RandomXS128.java:110) ~[desktop-1.0.jar:?]
at com.badlogic.gdx.math.RandomXS128.nextInt(RandomXS128.java:99) ~[desktop-1.0.jar:?]
at com.megacrit.cardcrawl.random.Random.random(Random.java:52) ~[desktop-1.0.jar:?]
at com.megacrit.cardcrawl.cards.CardGroup.getRandomCard(CardGroup.java:570) ~[?:?]
at HalationCode.relics.katawashoujo.PrussianBluePaint.betterOnSmith(PrussianBluePaint.java:44) ~[Halation.jar:?]
at com.evacipated.cardcrawl.mod.stslib.patches.relicInterfaces.BetterOnSmithRelicPatch.Insert(BetterOnSmithRelicPatch.java:26) ~[StSLib.jar:?]
at com.megacrit.cardcrawl.vfx.campfire.CampfireSmithEffect.update(CampfireSmithEffect.java:58) ~[?:?]
at com.megacrit.cardcrawl.dungeons.AbstractDungeon.update(AbstractDungeon.java:2640) ~[?:?]
at com.megacrit.cardcrawl.core.CardCrawlGame.update(CardCrawlGame.java:878) ~[?:?]
at com.megacrit.cardcrawl.core.CardCrawlGame.render(CardCrawlGame.java:429) [?:?]
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:225) [?:?]
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:126) [desktop-1.0.jar:?]