Prevent state from being actorless

[NicoooByte]

OS
Windows 10

Unity
Unity 2021.2.0f1

DialogueGraph
2.0.0

Description
If the state has no actor, the following error occurs:

System.Collections.Generic.Dictionary`2[TKey,TValue].get_Item (TKey key) (at <7b5f9a2f7db343a4ab54846ed680277b>:0)
DialogueGraph.Runtime.RuntimeDialogueGraph.GetCurrentActor () (at Library/PackageCache/com.github.teodorvecerdi.dialoguegraph@2.0.0/Runtime/RuntimeDialogueGraph.cs:68)

originating from "RuntimeDialogueGraph.cs"

public ActorData GetCurrentActor() {
            var currentNode = DlogObject.NodeDictionary[currentNodeGuid];
            if (currentNode.Type != NodeType.NPC) return null;
            var currentNodeActorGuid = currentNode.ActorGuid;
            var actor = CurrentData.ActorData[CurrentData.ActorDataIndices[currentNodeActorGuid]]; // <- Throws error
            return actor;
        }

[123tris]

The reason this throws an error is because GetCurrentActor is called when the current node is an NPC node but doesn't actually contain actor data. The solution to this is simple. When retrieving currentNode we should check if currentNode.ActorGuid is null or an empty string. Pull-request I submitted that fixes it:
#16

[TeodorVecerdi]

Thanks for the fix @123tris!
I'll close this issue once I release a new version of DialogueGraph containing the fix 👍