Should avoid unexpected error if trying to tostring a method that's now filtered out.

Clearing out callback cache when a world is unloaded.

src/main/scala/li/cil/oc/common/EventHandler.scala

@@ -25,6 +25,7 @@ import li.cil.oc.common.tileentity.traits.power
 import li.cil.oc.integration.Mods
 import li.cil.oc.integration.util
 import li.cil.oc.server.component.Keyboard
+import li.cil.oc.server.machine.Callbacks
 import li.cil.oc.server.machine.Machine
 import li.cil.oc.server.{PacketSender => ServerPacketSender}
 import li.cil.oc.util.ExtendedWorld._
@@ -357,6 +358,8 @@ object EventHandler {
       e.world.loadedEntityList.collect {
         case host: MachineHost => host.machine.stop()
       }
+
+      Callbacks.clear()
     }
   }
 

src/main/scala/li/cil/oc/server/machine/Callbacks.scala

@@ -27,6 +27,12 @@ object Callbacks {
     case _ => cache.getOrElseUpdate(host.getClass, dynamicAnalyze(host))
   }
 
+  // Clear the cache; used when world is unloaded, mostly to allow reacting to
+  // stuff (aka configs) that may influence which @Callbacks are enabled.
+  def clear(): Unit = {
+    cache.clear()
+  }
+
   def fromClass(environment: Class[_]) = staticAnalyze(environment)
 
   private def dynamicAnalyze(host: Any) = {

src/main/scala/li/cil/oc/server/machine/luac/ComponentAPI.scala

@@ -83,7 +83,7 @@ class ComponentAPI(owner: NativeLuaArchitecture) extends NativeLuaAPI(owner) {
       withComponent(lua.checkString(1), component => {
         val method = lua.checkString(2)
         val methods = machine.methods(component.host)
-        owner.documentation(() => methods(method).doc)
+        owner.documentation(() => Option(methods.get(method)).map(_.doc).orNull)
       })
     })
     lua.setField(-2, "doc")

src/main/scala/li/cil/oc/server/machine/luaj/ComponentAPI.scala

@@ -71,7 +71,7 @@ class ComponentAPI(owner: LuaJLuaArchitecture) extends LuaJAPI(owner) {
       withComponent(args.checkjstring(1), component => {
         val method = args.checkjstring(2)
         val methods = machine.methods(component.host)
-        owner.documentation(() => methods(method).doc)
+        owner.documentation(() => Option(methods.get(method)).map(_.doc).orNull)
       })
     })