Fix a case when the tuple length is not known

Author: tomasr8

Python/optimizer_bytecodes.c

@@ -376,8 +376,15 @@ dummy_func(void) {
             assert(PyLong_CheckExact(sym_get_const(ctx, right)));
             long index = PyLong_AsLong(sym_get_const(ctx, right));
             assert(index >= 0);
-            assert(index < sym_tuple_length(left));
-            res = sym_tuple_getitem(ctx, left, index);
+            int tuple_length = sym_tuple_length(left);
+            if (tuple_length == -1) {
+                // Unknown length
+                res = sym_new_not_null(ctx);
+            }
+            else {
+                assert(index < tuple_length);
+                res = sym_tuple_getitem(ctx, left, index);
+            }
         }
         else {
             res = sym_new_not_null(ctx);