[BUG] Unhandled default varbit value

[Macweese]

Describe the bug
Smithing items with Spacebar when preselected item is unset causes the following errors:

• NPE when fetching the smithing product
• ArithmeticException from attempting to divide by zero, since the smithing product is null, numberOfBarsForSelectedItem is 0

To Reproduce
Steps to reproduce the behavior:

1. Don't have a preselected product
2. Smith using the Spacebar
3. See error

Log

2024-08-09 20:07:49 KST [Client] WARN  n.runelite.client.eventbus.EventBus - Uncaught exception in event subscriber
java.lang.NullPointerException: null
  at com.github.calebwhiting.runelite.plugins.actionprogress.detect.SmithingDetector.onScriptPreFired(SmithingDetector.java:129)
  at net.runelite.client.eventbus.EventBus$Subscriber.invoke(EventBus.java:70)
  at net.runelite.client.eventbus.EventBus.post(EventBus.java:223)
  at net.runelite.client.callback.Hooks.post(Hooks.java:202)
  at client.se(client.java:58236)
  at mb.ag(mb.java:63253)
  at no.ad(no.java:52375)
  at av.cl(av.java:5370)
  at pk.on(pk.java:13057)
  at client.kr(client.java:27333)
  at client.is(client.java:3285)
  at client.bw(client.java:1215)
  at bs.ue(bs.java:388)
  at bs.nr(bs.java)
  at bs.run(bs.java:23449)
  at java.base/java.lang.Thread.run(Thread.java:834)
2024-08-09 20:07:49 KST [Client] WARN  n.runelite.client.eventbus.EventBus - Uncaught exception in event subscriber
java.lang.ArithmeticException: / by zero
  at com.github.calebwhiting.runelite.plugins.actionprogress.detect.SmithingDetector.keyPressed(SmithingDetector.java:77)
  at net.runelite.client.input.KeyManager.processKeyPressed(KeyManager.java:89)
  at net.runelite.client.callback.Hooks.keyPressed(Hooks.java:350)
  at ar.keyPressed(ar.java:9416)
  at java.desktop/java.awt.Component.processKeyEvent(Component.java:6590)
  at java.desktop/java.awt.Component.processEvent(Component.java:6409)
  at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5008)
  at java.desktop/java.awt.Component.dispatchEvent(Component.java:4840)
  at java.desktop/java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1950)
  at java.desktop/java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:870)
  at java.desktop/java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1139)
  at java.desktop/java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:1009)
  at java.desktop/java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:835)
  at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:4889)
  at java.desktop/java.awt.Component.dispatchEvent(Component.java:4840)
  at net.runelite.client.plugins.dialogues.DialoguePlugin.pressKey(DialoguePlugin.java:162)
  at net.runelite.client.plugins.dialogues.DialoguePlugin.onWidgetLoaded(DialoguePlugin.java:151)
  at net.runelite.client.eventbus.EventBus$Subscriber.invoke(EventBus.java:70)
  at net.runelite.client.eventbus.EventBus.post(EventBus.java:223)
  at net.runelite.client.callback.Hooks.post(Hooks.java:202)
  at client.pr(client.java:10226)
  at av.cl(av.java:5373)
  at pk.on(pk.java:13057)
  at client.kr(client.java:27333)
  at client.is(client.java:3285)
  at client.bw(client.java:1215)
  at bs.ue(bs.java:388)
  at bs.nr(bs.java)
  at bs.run(bs.java:23449)
  at java.base/java.lang.Thread.run(Thread.java:834)
2024-08-09 20:07:49 KST [Client] WARN  n.runelite.client.eventbus.EventBus - Uncaught exception in event subscriber
java.lang.NullPointerException: null
  at com.github.calebwhiting.runelite.plugins.actionprogress.detect.SmithingDetector.onScriptPreFired(SmithingDetector.java:129)
  at net.runelite.client.eventbus.EventBus$Subscriber.invoke(EventBus.java:70)
  at net.runelite.client.eventbus.EventBus.post(EventBus.java:223)
  at net.runelite.client.callback.Hooks.post(Hooks.java:202)
  at client.se(client.java:58236)
  at mb.ag(mb.java:63253)
  at no.ad(no.java:52375)
  at df.aq(df.java:101)
  at client.is(client.java:3642)
  at client.bw(client.java:1215)
  at bs.ue(bs.java:388)
  at bs.nr(bs.java)
  at bs.run(bs.java:23449)
  at java.base/java.lang.Thread.run(Thread.java:834)