Loosen what is allowed in whilestmt38...

Fixes #498

Author: rocky

test/bytecode_3.8/03_while_bug.pyc

@@ -0,0 +1,9 @@
+# See https://github.com/rocky/python-uncompyle6/issues/498
+# Bug was in not allowing _stmts in whilestmt38
+import time
+
+r = 0
+while r == 1:
+    print(time.time())
+    if r == 1:
+        r = 0

test/simple_source/bug38/03_while_bug.py

@@ -144,7 +144,7 @@ def customize_for_version38(self, version):
             "whilestmt38": (
                 "%|while %c:\n%+%c%-\n\n",
                 (1, ("bool_op", "testexpr", "testexprc")),
-                (2, ("l_stmts", "l_stmts_opt", "pass")),
+                (2, ("_stmts", "l_stmts", "l_stmts_opt", "pass")),
             ),
             "whileTruestmt38": (
                 "%|while True:\n%+%c%-\n\n",