Move builtin rewrite assert

Author: msimacek

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

@@ -390,21 +390,21 @@ public synchronized PFunction convertToBuiltin(PFunction func) {
             Signature signature = func.getSignature();
             PFunction builtinFunc;
             FunctionRootNode functionRootNode = (FunctionRootNode) func.getFunctionRootNode();
-            assert !functionRootNode.isPythonInternal() : "a function cannot be annotated as builtin twice";
-            functionRootNode.setPythonInternal(true);
             if (signature.getParameterIds().length > 0 && signature.getParameterIds()[0].equals("self")) {
                 /*
                  * If the first parameter is called self, we assume the function does explicitly
                  * declare the module argument
                  */
                 builtinFunc = func;
+                functionRootNode.setPythonInternal(true);
             } else {
                 /*
                  * Otherwise, we create a new function with a signature that requires one extra
                  * argument in front. We actually modify the function's AST here, so the original
                  * PFunction cannot be used anymore (its signature won't agree with it's indexed
                  * parameter reads).
                  */
+                assert !functionRootNode.isPythonInternal() : "a function cannot be rewritten as builtin twice";
                 functionRootNode = functionRootNode.rewriteWithNewSignature(signature.createWithSelf(), new NodeVisitor() {
 
                     public boolean visit(Node node) {