Fix: Use 'uninitializedBody' to copy function root node with new arity.

Author: fangerer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/modules/BuiltinFunctions.java

@@ -1760,8 +1760,8 @@ public boolean visit(Node node) {
                  */
                 FunctionRootNode functionRootNode = (FunctionRootNode) func.getFunctionRootNode();
                 assert !functionRootNode.isRewritten() : "a function cannot be annotated as builtin twice";
-                functionRootNode.setRewritten();
                 functionRootNode = functionRootNode.copyWithNewArity(arity.createWithSelf());
+                functionRootNode.setRewritten();
                 functionRootNode.accept(new NodeVisitor() {
                     public boolean visit(Node node) {
                         if (node instanceof ReadVarArgsNode) {

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/nodes/function/FunctionRootNode.java

@@ -80,8 +80,8 @@ public FunctionRootNode(PythonLanguage language, SourceSection sourceSection, St
     }
 
     public FunctionRootNode copyWithNewArity(Arity newArity) {
-        FunctionRootNode copy = new FunctionRootNode(getLanguage(PythonLanguage.class), getSourceSection(), functionName, isGenerator, getFrameDescriptor(), body, executionCellSlots, newArity);
-        copy.setRewritten();
+        FunctionRootNode copy = new FunctionRootNode(getLanguage(PythonLanguage.class), getSourceSection(), functionName, isGenerator, getFrameDescriptor(), uninitializedBody, executionCellSlots,
+                        newArity);
         return copy;
     }