Partially fix ast command

Author: enebo

bin/ast

@@ -193,7 +193,7 @@ def ir_setup(root)
 
   builder = org.jruby.ir.IRBuilder
 
-  scope = builder.new(manager).build_root(root)
+  scope = builder.build_root(manager, root)
   passes = manager.get_compiler_passes(scope)
   [scope, passes]
 end

core/src/main/java/org/jruby/ir/IRScope.java

@@ -239,6 +239,7 @@ public boolean equals(Object other) {
     }
 
     protected void addChildScope(IRScope scope) {
+        if (lexicalChildren == null) lexicalChildren = new ArrayList<>();
         lexicalChildren.add(scope);
     }