parseText throw ArrayIndexOutOfBoundsException when build with an empty map

```kotlin
val acdat = AhoCorasickDoubleArrayTrie<String>()
acdat.build(emptyMap())

println(acdat.parseText("uhers")) // java.lang.ArrayIndexOutOfBoundsException
```

![image](https://user-images.githubusercontent.com/10527522/129342845-65522daf-3e64-48ad-81cc-8350addf9b94.png)
