Fix CommandPart.init

SpigotCore_Main/src/de/steamwar/command/CommandPart.java

@@ -44,6 +44,9 @@ public class CommandPart {
     private CommandPart next = null;
 
     public CommandPart(TypeMapper<?> typeMapper, GuardChecker guard, Class<?> varArgType, String optional, GuardCheckType guardCheckType) {
+        if (guardCheckType == GuardCheckType.TAB_COMPLETE) {
+            throw new IllegalArgumentException("Tab complete is not allowed as a guard check type!");
+        }
         this.typeMapper = typeMapper;
         this.guard = guard;
         if (optional != null && varArgType != null) {